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Chickenpox Overview

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Chickenpox: The Disease

Chickenpox (varicella) is an illness caused by the varicella zoster virus, a DNA virus that is part of the herpes virus family and associated with shingles. The virus first presents as a chickenpox infection; however, if the virus reactivates, it will present as a shingles infection. Chickenpox is transmitted through direct contact with chickenpox blisters, by inhaling particles from the chickenpox blisters, and possibly from contact with respiratory secretions infected with the virus. Symptoms of chickenpox generally begin between 10 and 21 days following exposure to the virus and the illness typically lasts between 5 and 10 days. The varicella virus is found only in humans and outbreaks generally occur between March and May in the United States. Learn more about Chickenpox…

Chickenpox Vaccine

There are two live virus vaccines for chickenpox licensed for use in the U.S. by the FDA: Varivax, a live varicella (chickenpox) virus vaccine manufactured by Merck; and ProQuad (MMRV), a live virus vaccine containing measles, mumps, rubella and varicella (chickenpox), also manufactured by Merck. There is a higher risk of seizure following MMRV vaccination if this vaccine is administered as the first dose, when compared to the administration of separate doses of MMRII and varicella vaccines. The CDC recommends children receive a first dose of chickenpox vaccine between 12 and 15 months and a second dose between 4 and 6 years. The CDC also recommends two doses of chickenpox vaccine be administered 4 to 8 weeks apart to all school-aged students, post-secondary aged students, and all healthy adults who lack immunity to chickenpox.Learn more about Chickenpox vaccine…

Chickenpox Quick Facts

Chickenpox

Chickenpox (Varicella) is a highly-contagious infection that is generally mild in most children;
Chickenpox is transmitted through direct contact with, or by inhaling particles from chickenpox blisters. It may also be spread through respiratory secretions of a person infected with the virus;
Recovery from chickenpox confers long lasting natural immunity and immunocompetent individuals rarely experience a second attack. Re-exposure to chickenpox has been found to boost immunity and reduce the risk of shingles infection in older children and adults.Continue reading quick facts…

Chickenpox Vaccine

Mild side effects, such as redness, rash, or pain at the injection site, as well as fever, have been reported following chickenpox vaccination. More serious side effects of chickenpox vaccine include meningitis, pneumonia, seizures, full body rash, allergic reaction, and death.Mild side effects following MMRV vaccination include rash, redness, or pain at the injection site, fever and swelling of the glands in the neck or cheeks. More serious side effects of MMRV vaccine may include loss of hearing, meningitis, pneumonia, full body rash, seizure, coma, brain damage, severe allergic reaction, and death;
Chickenpox vaccine is reported to be between 80 and 85 percent effective at preventing chickenpox and more than 95 percent effective at preventing severe illness.The widespread use of chickenpox vaccine in the U.S. has substantially increased the rate of shingles infections in adults, as a natural boost of immunity from exposure to chickenpox in the environment is no longer occurring; Continue reading quick facts…

NVIC encourages you to become fully informed about chickenpox and the chickenpox vaccine by reading all sections in the table of contents, which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

What is chickenpox?

Chickenpox (varicella) is an illness caused by the varicella zoster virus, a DNA virus that is part of the herpes virus family (Alphaherpesvirinae) and associated with shingles (herpes zoster). The virus first presents as a chickenpox infection, however, as the virus is able to remain in the sensory nerve ganglia of the body after the first infection, it has the potential to reactivate. If the virus reactivates, it will present as a shingles infection. The varicella virus is found only in humans and outbreaks generally occur between March and May in the United States.

Chickenpox is transmitted through direct contact with chickenpox blisters, by inhaling particles from the chickenpox blisters, and possibly from contact with respiratory secretions infected with the virus. Symptoms of chickenpox generally begin between 10- and 21-days following exposure to the virus and the illness typically lasts between 5 and 10 days. In adults, initial chickenpox symptoms can include headache, fever, loss of appetite and fatigue. These symptoms usually occur 1 to 2 days prior to the onset of a rash; however, in children, the rash is often the first sign of infection.

When the chickenpox rash occurs, it usually begins with raised red or pink itchy bumps (papules). These bumps generally last a few days before they progress to become fluid-filled blisters (vesicles). After about a day or so, the blisters break open, leak and eventually crust and scab over. The rash usually starts on the head, then spreads to the trunk, and eventually to the arms and legs. The rash can also be present in the eyes, throat, and genitals. As the rash appears over several days, chickenpox lesions can be present on the body as papules, vesicles, and scabs simultaneously. On average, healthy children will usually have between 200 and 500 chickenpox lesions that are generally one to four millimeters in diameter.

Chickenpox infections can happen in vaccinated individuals but is often reported as a milder infection, with fewer than 50 skin lesions, and the rash frequently presents as papules instead of vesicles. Fever rates may also be lower among vaccinated individuals who develop chickenpox. Between 25-30 percent of persons who develop chickenpox after receiving one dose of chickenpox vaccine may still experience an illness similar to a natural chickenpox infection. Information on the presentation of breakthrough chickenpox illness among persons vaccinated with two doses of the vaccine is limited at this time. A person with breakthrough chickenpox is still contagious and can spread the illness on to others.

A person with breakthrough illness resulting in less than 50 lesions is believed to be two thirds less likely to transmit the illness than those who developed more than 50 lesions; however, the mild clinical presentation may delay a diagnosis. As a result, individuals with undiagnosed breakthrough chickenpox may potentially cause higher rates of transmission within the community by failing to take isolation precautions to prevent the spread of the illness to others.

Chickenpox is considered a mild infection; however, complications can occur. Complications from chickenpox may include viral and bacterial pneumonia, bacterial skin infections, encephalitis, cerebellar ataxia, septicemia, necrotizing fasciitis, toxic shock syndrome, osteomyelitis, and septic arthritis. Infants born to mothers infected with chickenpox between five days prior to and two days post-delivery, premature infants, pregnant women, and persons with immunosuppressive conditions are considered to be at highest risk of developing complications.

Prior to the introduction of the chickenpox vaccine, nearly everyone developed the infection as a child. Approximately 4 million cases of chickenpox occurred annually in the United States, and the majority of cases affected children under the age of 15. Children between one and four years were found to have the highest rates of chickenpox infections and were followed closely by children between five and nine years. Only seven percent of chickenpox infections occurred in adults. Chickenpox was removed from the list of nationally reportable diseases in 1981 but returned to the list in 2003. Chickenpox- related death have been nationally notifiable since 1999. In 2019, six chickenpox- associated deaths were reported in the United States. One chickenpox- related death was reported to the CDC in 2020.

Recovery from chickenpox confers long lasting natural immunity and immunocompetent individuals rarely experience a second attack. Re-exposure to the chickenpox virus will boost a person’s immune system and decrease their risk of shingles infection.

IMPORTANT NOTE: NVIC encourages you to become fully informed about Chickenpox and the Chickenpox vaccine by reading all sections in the Table of Contents , which contain many links and resources such as the manufacturer product information inserts, and to speak with one or more trusted health care professionals before making a vaccination decision for yourself or your child. This information is for educational purposes only and is not intended as medical advice.

Is chickenpox contagious?

Chickenpox (Varicella) is a highly contagious infection that is generally mild for most children.Chickenpox is transmitted through direct contact with or by inhaling particles from the chickenpox blisters. It may also possibly be spread through the respiratory secretions of a person infected with the virus. Less commonly, a person who lacks immunity to chickenpox can also develop the illness by coming into contact with a shingles rash.Symptoms of chickenpox generally begin between 10- and 21-days following exposure to the virus and the illness typically lasts between 5 and 10 days.

Initial chickenpox symptoms can include headache, fever, loss of appetite, and fatigue. When the chickenpox rash occurs, it usually begins with raised red or pink itchy bumps (papules). These bumps generally last a few days before progressing to become fluid-filled blisters (vesicles). After about a day or so, the blisters break open, leak and eventually crust and scab over.The rash usually starts on the head, then spreads to the trunk, and eventually to the arms and legs. The rash can also be present in the eyes, throat, and genitals.As the rash appears over several days, chickenpox lesions can be simultaneously present on the body as papules, vesicles, and scabs.

Chickenpox is considered contagious for 1 to 2 days prior to the onset of the rash and remains so until all lesions have become scabs. Individuals previously vaccinated with the chickenpox vaccine and who develop chickenpox are considered to be contagious until 24 hours following the final appearance of lesions. Chickenpox lesions in a person previously vaccinated with the chickenpox vaccine may not always crust over.

Previously vaccinated individuals who develop chickenpox are still contagious and can spread the infection to others.

What is the history of chickenpox in America and other countries?

Herpesvirologists believe that the chickenpox (varicella) virus originated in Africa millions of years ago. In 1767, English physician William Heberden definitively differentiated chickenpox from smallpox and reported lifelong immunity to the illness upon recovery from the infection. In 1875, Rudolf Steiner discovered that chickenpox was infectious to others after he took liquid from the chickenpox blisters of an infected individual and spread it to healthy volunteers. The first association between shingles and chickenpox was noted in 1888, after Von Bokay found that children with a negative history of chickenpox developed the infection after exposure to shingles. In 1954, Dr. Thomas Weller isolated the varicella virus in both chickenpox and shingles lesions.

In 1951, when the CDC reported on its plan to revise morbidity reporting by states, chickenpox was not considered significant enough of a disease to be listed as part of the “Minimum List for National Reporting.” Deaths related to chickenpox were still being reported and between 1950 and 1959, an average of 114 chickenpox-associated deaths were reported annually. When chickenpox became a nationally notifiable disease in 1972, 164,114 cases were reported to the CDC. Public health officials, however, estimated that nearly 4 million infections actually occurred each year, which resulted in approximately 100 deaths and 10,000 hospitalizations.

In the late 1970’s, the CDC became aware of a potential association between the use of aspirin during an illness such as chickenpox or influenza, and Reye syndrome, a rare illness that can affect the liver, blood, and brain, and lead to coma and brain death. By June of 1982, evidence supported these findings, which prompted the U.S. Surgeon General to issue a warning against the use of aspirin and aspirin-containing products by children during an influenza or chickenpox illness.

In 1981, chickenpox was removed from the weekly morbidity report, and individual states were encouraged to report the number of cases on an annual basis. This change in reporting requirements was noted by the CDC to coincide with a decrease in the number of states reporting chickenpox illness. In 1972, 46 states and the District of Columbia (D.C.) were reporting chickenpox cases on a weekly basis; however, by 1997, only 20 states and D.C. were submitting data, which significantly decreased the reliability of national chickenpox rates.

In the 25 years prior to the licensing of the chickenpox vaccine, there were a total of 2,262 deaths, an average of 90 deaths per year, associated with chickenpox infections. 59 percent of deaths occurred in adolescents and children under the age of 20, and death rates were highest among Caucasians. However, death rates, when compared to the number of infections, were found to be highest among adults, and were followed by children younger than 12 months of age. Death rates were also noted to be highest between March and May, and lowest between August and October.

From 1970 to 1994, the year prior to the licensing of the chickenpox vaccine, death from chickenpox decreased by between 51.3 and 72.2 percent among persons of all ages, but especially among adults who developed the illness. Death rates were found to be higher among foreign-born adults, especially those who had immigrated to the U.S. from tropical climates where chickenpox infections are frequently seen in adults rather than in children. 27.5 percent of chickenpox-associated death certificates reported a pre-existing medical condition, with cancer being the most frequently listed comorbidity.

Death from chickenpox-related pneumonia was most frequently reported (27.6 percent) and was followed by central nervous system (CNS) complications (21.1 percent). Of these CNS complications, nearly 9 percent were confirmed to be the result of Reye syndrome, acknowledged by the U.S. Surgeon General in 1982 to be associated with the use of aspirin-containing products in children with chickenpox.During this time period, the overall annual death rate from chickenpox was estimated at 0.4 deaths per 1 million population.

In 1996, at the time of the CDC’s Advisory Committee on Immunization Practices (ACIP) recommendation for routine administration of the newly licensed chickenpox vaccine, the CDC reported that an estimated 3.7 million cases of chickenpox occurred annually. However, as the illness was not nationally notifiable, the CDC also admitted that surveillance data was limited and estimated that only 4-5 percent of illnesses were actually reported. In response, the CDC established 3 active surveillance sites to monitor the impact of the vaccine, in Antelope Valley, California, Travis County, Texas and West Philadelphia, PA.

According to the CDC, by 2000, as chickenpox vaccination rates climbed to 74-84 percent of all 19 to 35-month olds in the active surveillance site communities, chickenpox infections decreased significantly. In 2003, the year when chickenpox infections returned to the nationally notifiable disease list, only 20,948 cases were reported. The CDC also reported that for the four states (Texas, Michigan, Illinois, and West Virginia) which had consistently submitted chickenpox infection data since 1990, each had reported the lowest number of cases on record. Increased use of the chickenpox vaccine, especially among preschool children, was credited for the decrease.

Active surveillance of chickenpox continued at two of the three original surveillance sites set up in 1995 to monitor the impact of the chickenpox vaccine. From data collected between 1996 and 2005, site investigators noted that as vaccination rates increased to approximately 90 percent among the two remaining surveillance sites, the number of chickenpox infections also increased among vaccinated individuals, from two percent to 56 percent. The age of the illness of those infected also shifted, with most infections occurring in children between 9 and 11 years, instead of in younger children, who were previously noted to have higher infection rates prior to the introduction of the chickenpox vaccine.

After recovery from chickenpox, the virus will remain dormant in the sensory nerve ganglia of the body.The virus, however, can re-activate as shingles (herpes zoster), a painful rash that typically presents on one side of the body or face, and can result in complications including vision loss, balance or hearing issues, and postherpetic neuralgia (PHN) – a condition which causes severe and often long-lasting pain at the site of the shingles rash.

Exposure to a circulating strain of chickenpox virus (e.g. contact with a sick child) boosts the immune response in a person with a prior history of chickenpox illness, and this can delay or even prevent shingles infection. When routine use of the chickenpox vaccine was recommended in 1996, the CDC reported that only 15 percent of adults would ever experience shingles at some point in their lifetime. The FDA, in their summary report to support the approval of the chickenpox vaccine, expressed concerns that the vaccine might lead to a significant rise in shingles cases and recommended that health officials monitor shingles rates following the vaccine’s introduction.

The CDC, however, chose not to monitor shingles infections at any of the three active surveillance sites in 1995. Five years later, in 2000, shingles surveillance was finally added to California’s Antelope Valley Varicella Active Surveillance Project (AV-VASP), at a time when chickenpox rates had declined by 70 percent. By 2000, the number of reported shingles infections had already increased dramatically in adults 20 to 69 years, and children with a prior history of chickenpox illness were found to have shingles rates similar to the adult population. Over a three-year period, from 2000 to 2002, the number of reported shingles cases increased by 56 percent, an 18 percent yearly increase.Additionally, a CDC-sponsored study completed in Massachusetts found that between 1998 and 2003, as chickenpox vaccine use increased and chickenpox infection rates decreased, the overall rate of shingles infections increased by 141 percent among all age groups. The incidence of shingles among adults between 25 and 44 years increased by 161 percent, while rates among children and young adults aged 1 to 24 years increased by 152 percent.

From 2001 to 2005, multiple outbreaks of chickenpox illness among fully-vaccinated school children were reported and vaccinated students were frequently found to be responsible for the outbreaks. The CDC reported the vaccine to be between 72 and 85 percent effective; however, in some schools, up to 40 percent of vaccinated students in one classroom developed chickenpox. While many cases were reportedly mild, up to 30 percent were not, and vaccinated students were found to have chickenpox symptoms similar to children who developed natural chickenpox illness. At least two chickenpox-related deaths were reported among vaccinated children who developed chickenpox as a result of vaccine failure.

The CDC reported that vaccinated children with breakthrough illness (resulting in less than or equal to 50 lesions) were two-thirds less likely to transmit the illness when compared to vaccinated children who developed more than 50 lesions; however, they also acknowledged that the illness could be mild enough to delay diagnosis and isolation. As a result, undiagnosed cases of mild chickenpox infections had the potential to result in a higher rate of transmission within a community.

In June 2006, in response to the significant rise in chickenpox illness among vaccinated children, ACIP voted to recommend a second dose of chickenpox vaccine be administered to all children prior to school entry, at age 4-6 years, and recommended that all persons previously vaccinated with one dose of chickenpox vaccine receive a second dose.

Following the booster dose recommendation, the CDC determined that the two remaining chickenpox active surveillance sites were not sufficient enough to monitor the impact of the two-dose chickenpox vaccine recommendation and opted instead to examine chickenpox data collected from the National Notifiable Diseases Surveillance System (NNDSS). However, as chickenpox was not a nationally notifiable disease until 2003, the NNDSS could not be considered a reliable data source for chickenpox surveillance data.

As a result, the CDC came up with ad hoc criteria to decide whether a particular state’s data could, in fact, be considered an accurate reflection of the true number of reported chickenpox cases. Only states reporting at least one case of chickenpox per 100,000 population for at least three consecutive years, between 2000 and 2010, were considered in the analysis of NNDSS data. This meant that only 31 of the 39 states reporting chickenpox infections to NNDSS could be included. From the 31 states, the CDC reported that chickenpox infections decreased by 43 percent between 2000 and 2005, following the single-dose vaccine recommendation, and by 72 percent between 2006 and 2010 following the booster dose recommendation. Overall, chickenpox rates were reported to have decreased by 79 percent between 2000 and 2010.

In 2010, 15,427 chickenpox infections were reported to the NNDSS. Vaccination status was known for 32 percent of all reported cases, and of these cases, 60 percent occurred in persons with a prior history of chickenpox vaccination. Of the cases which occurred among previously vaccinated individuals, only half were considered mild. Four chickenpox-related deaths were reported in 2010.

While cases and outbreaks of chickenpox have decreased, the number of shingles infections have significantly increased, with the CDC reporting that they do not know the reason for this increase. Several published studies, however, note that shingles cases have increase significantly since the introduction and uptake of the chickenpox vaccine. While shingles is not, and has never been a nationally notifiable disease, the CDC currently reports that 33 percent of people are at risk for developing shingles in their lifetime, up from the 15 percent previously reported in 1996, at the time of the ACIP recommendation for routine use of the chickenpox vaccine.

In 2019, 8,297 cases of chickenpox and 6 deaths were reported by 39 states, the District of Columbia, and 2 U.S. territories. One death and 2,952 chickenpox cases were reported in 2020.

Globally, the World Health Organization (WHO) reports that in temperate climates, most cases of chickenpox occur before the age of ten. The WHO also reports the illness to be mild and generally self-limiting, but states that severe complications can occur, more frequently among infants and persons with immunosuppression.

Many European countries do not recommend routine use of the chickenpox vaccine, and most individuals residing in these countries will develop the illness during childhood. In the United Kingdom (UK), where routine chickenpox vaccination is not recommended, health officials consider the illness to be mild and report that most infected children recover within a week, without the need to see a doctor. UK public health officials state their decision to not routinely recommend chickenpox vaccine was based on concerns that a decrease in chickenpox rates would put unvaccinated children at risk of developing the illness as adults, when complications can be more severe. They also report that widespread use of the chickenpox vaccine would significantly increase the rate of shingles among adults.

Can chickenpox cause injury and/or death?

For most people, chickenpox is a mild infection which lasts between 5 and 10 days. However, in rare cases, complications can occur. The most common complications include bacterial infections of the soft tissues and skin, which occur primarily in children; and pneumonia, more frequently seen among adults who develop the infection. Complications of bacterial infections can include bacterial pneumonia, septicemia, osteomyelitis, septic arthritis, necrotizing fasciitis, and toxic shock syndrome. Infrequently, complications such as central nervous system disturbances, including cerebellar ataxia, encephalitis, and aseptic meningitis may also occur. Children who take aspirin or aspirin-containing products during a chickenpox infection are at a higher risk for developing Reye syndrome, an illness which affects the liver, blood, and brain, and can lead to coma and brain death.

Additional rare complications include Guillain-Barre Syndrome (GBS), transverse myelitis, hemorrhagic varicella, myocarditis, hepatitis, glomerulonephritis, purpura fulminans, orchitis, uveitis, iritis, thrombocytopenia, and death.

Persons with immunosuppressive conditions who become infected with chickenpox may be at risk for visceral dissemination, a complication where the internal organs become infected with chickenpox. Visceral dissemination can lead to encephalitis, hepatitis, pneumonia, and disseminated intravascular coagulopathy (DIC).

Rarely, congenital varicella syndrome (CVS) can also occur if a pregnant woman develops chickenpox in the early part of a pregnancy. Infants born with this condition can have abnormalities of the arms, legs, hands, feet, eyes, brain, skin, and other areas of the body. If a pregnant woman develops chickenpox during the first 20 weeks of gestation, the risk of an infant developing CVS is estimated to be between 0.4 and 2 percent. The risk of CVS after a case of maternal chickenpox in the second trimester is believed to be at less than one percent, and no risk of CVS exists if a mother develops chickenpox during the third trimester of pregnancy.

Newborn infants whose mothers developed chickenpox from five days before to two days after delivery are at a higher risk for the development of neonatal chickenpox, that, if left untreated, may lead to death.

Who is at highest risk for getting chickenpox?

Chickenpox is highly contagious and can be easily transmitted through contact with the chickenpox rash or respiratory secretions spread through the air by sneezing or coughing. Persons who are considered to be at higher risk for infection include:

persons who have not had chickenpox or the vaccine
individuals who attend or work in a day-care or school setting
persons who reside with children

Individuals previously vaccinated with the chickenpox vaccine may still develop chickenpox, however, the infection may be milder. Most people who get chickenpox develop lifelong immunity, however, while rare, it is possible to have the infection more than once. Individuals who lack immunity to chickenpox can also develop the illness by coming into contact with a shingles rash.

Who is at highest risk for suffering complications from chickenpox?

Individuals considered most at risk for developing complications from chickenpox include:

Pregnant women who are not immune to the infection. Pregnant women may be at higher risk of developing complications, especially pneumonia. Infants born to women who develop chickenpox during the first or early part of the second trimester have a rare chance of developing congenital varicella disease (CVD), which may result in low birth weight, scarring of the skin, and brain, limb, and eye abnormalities. CVD, however, is so rare that two large studies on the impact of varicella disease during pregnancy showed no increase in congenital anomalies when compared with control groups.
Newborn infants whose mothers developed chickenpox five days before to two days following delivery. Infants exposed to chickenpox at birth or shortly after are at a higher risk for developing neonatal chickenpox. Neonatal chickenpox complications can be severe or even fatal.
Hospitalized premature infants born at or more than 28 weeks gestation to mothers who are not immune to chickenpox.
Hospitalized premature infants born before 28 weeks gestation.
Persons who are immunocompromised and lack immunity. This includes:
- Individuals with immune system disorders, including cellular immune-deficiencies;
- Persons taking immunosuppressive medications including chemotherapeutic agents or high-dose steroids;
- Individuals with lymphoma or leukemia.

Persons with compromised immune systems who develop chickenpox may be at risk of visceral dissemination (chickenpox involving the internal organs), a complication which may lead to encephalitis, hepatitis, pneumonia, and disseminated intravascular coagulopathy (DIC). Immunocompromised individuals may also be at risk of having chickenpox for a longer period of time with a greater number of lesions, with lesions that may bleed.

Children who are HIV-positive may develop an atypical chickenpox rash which might persist for weeks or even months. Further, HIV-positive children are at high risk of shingles and recurrent chickenpox illness. Most HIV-positive adults, however, have previously been exposed to chickenpox illness, and as a result, the infection is not commonly found in this population. When it does occur, complications such as hepatitis and encephalitis, may be more severe.

Can Chickenpox be prevented and are there treatment options?

There are several home treatments that can help relieve chickenpox symptoms and prevent skin infections. Calamine lotion, oatmeal baths, and the use of antihistamine medications may help to relieve some of the itching. It may also be helpful to wear loose fitting cotton clothing. Refraining from scratching chickenpox lesions can reduce the risk of skin infections.

Non-aspirin medications, such as acetaminophen, can be used to relieve fever from chickenpox. Aspirin or aspirin-containing products should not be used in children with chickenpox due to an association between aspirin and Reye syndrome, a severe disease which affects the liver, blood, and brain, and can result in death.

For most people, chickenpox is a mild infection that will resolve on its own. However, it is important to seek out medical attention for the following symptoms:

The chickenpox rash becomes tender, warm, or very red. This may be a sign of a bacterial skin infection
The rash has spread to one or both eyes
Vomiting
Shortness of breath
Dizziness
Stiff neck
Involuntary muscle movements
Fever over 102 degrees

Persons who are not immune to chickenpox and considered at a high risk of infection, especially severe infection, can be administered varicella-zoster immune globulin to prevent the illness. This product should be administered as soon as possible or within 10 days of exposure to chickenpox. Physicians can also consider prescribing an oral anti-viral medication, such as Acyclovir, for persons considered at high risk for developing a serious chickenpox infection. These persons include:

healthy persons over the age of 12
persons receiving long-term salicylate (aspirin) therapy
individuals receiving intermittent, short, or aerosolized treatments with corticosteroids
persons with chronic lung and skin disorders

For the best results, treatment with oral anti-viral medication should begin within 24 hours of the appearance of the chickenpox rash. Anti-viral medications are not recommended for use in healthy children who are not experiencing complications from the illness.

Persons with severe varicella disease and those considered to be immunocompromised are recommended to receive Acyclovir by intravenous infusion (IV).

What is chickenpox vaccine?

Varivaxis a live, attenuated vaccine that contains the Oka/Merck strain of varicella (chickenpox) virus. This virus was taken from a child with wild-type chickenpox, inserted into human embryonic lung cell cultures, adapted to and grown in embryonic guinea pig cell cultures and then propagated in human diploid cell cultures (WI-38- a human diploid cell line derived from the lung tissue of a three-month human female embryo).Further passage of the chickenpox virus for vaccine usage was performed in human diploid cell cultures (MRC-5 cells- a human cell line developed in 1966 from lung tissue taken from a 14 week old male aborted fetus)that Merck has declared to be free of adventitious agents.

Varivax is a lyophilized preparation containing glutamate, sucrose, phosphate, and processed gelatin as stabilizers. When reconstituted as directed and stored at room temperature for a maximum of 30 minutes, each approximately 0.5mL dose of Varivax contains a minimum of 1,350 plaque-forming units (PFU) of Oka/Merck varicella virus. Each 0.5-mL dose contains hydrolyzed gelatin, monosodium L-glutamate (MSG), sodium chloride, sucrose, sodium phosphate dibasic, potassium phosphate monobasic, and potassium chloride. Varivax also contains residual components of MRC-5 cells, including DNA, protein, and trace quantities of sodium phosphate monobasic, neomycin, EDTA, and fetal bovine serum. The vaccine is approved to be administered both subcutaneously and intramuscularly, to be given immediately after reconstitution.

ProQuad vaccine is licensed and recommended for use in children aged 12 months to 12 years of age. ProQuad (MMRV) is a combined, attenuated, live virus vaccine containing measles, mumps, rubella, and varicella viruses. ProQuad is a sterile lyophilized preparation of the components of M-M-R II (Measles, Mumps, and Rubella Virus Vaccine Live), and varicella virus vaccine live, the Oka/Merck strain of varicella-zoster virus propagated in MRC-5 cells.

The growth medium for measles and mumps found in ProQuad is a buffered salt solution containing vitamins and amino acids and it is supplemented with fetal bovine serum containing sucrose, phosphate, glutamate, recombinant human albumin, and neomycin. The growth medium for rubella is a buffered salt solution containing vitamins and amino acids and supplemented with fetal bovine serum containing recombinant human albumin and neomycin. Sorbitol and hydrolyzed gelatin stabilizer are added to the individual virus harvests. The Oka/Merck strain of the live attenuated varicella virus, initially obtained from a child with wild-type varicella, introduced into human embryonic lung cell cultures, adapted to and propagated in embryonic guinea pig cell cultures and finally propagated in human diploid cell cultures (WI-38), is then added to the measles, mumps, and rubella vaccine. This vaccine is approved to be given by either subcutaneous or intramuscular injection.

According to Merck, ProQuad vaccine is screened for adventitious agents. Each dose of ProQuad contains sucrose, hydrolyzed gelatin, sorbitol, MSG, sodium phosphate, human albumin, sodium bicarbonate, potassium phosphate and chloride, neomycin, bovine calf serum, chick embryo cell culture, WI-38 human diploid lung fibroblasts and MRC-5 cells. ProQuad also contains a higher amount of Oka/Merck strain varicella plaque forming units (PFU) than Varivax, the single antigen varicella vaccine.

The ProQuad vaccine package insert states that one month should lapse between administration of ProQuad and another measles-containing vaccine such as MMRII and at least three months should lapse between ProQuad and any varicella containing vaccine.

The CDC recommends children receive a first dose of chickenpox vaccine between 12 and 15 months and a second dose between 4 and 6 years. The CDC also recommends two doses of chickenpox vaccine be administered 4 to 8 weeks apart to all school-aged students, post-secondary aged students, and all healthy adults who lack immunity to chickenpox.

What is the history of Chickenpox vaccine use in America and other countries?

The first live attenuated chickenpox vaccine was developed by Dr. Michiaki Takahashi in Japan. The virus was isolated from the fluid-filled blisters of a three-year-old child with typical chickenpox illness. The Oka strain of the chickenpox virus, named after the family from whom the virus was acquired, was then cultivated in guinea-pig embryo cultures and tested on a small number of children between 1 and 10 years of age. Scientists further developed the vaccine by taking the attenuated virus previously cultivated in guinea-pig embryo cultures and propagating it in WI-38 cells, a human diploid cell line derived from the lung tissue of an aborted three-month human female embryo.

Takahaski’s experimental chickenpox vaccine was initially tested in 1974 on 23 susceptible children, after a case of chickenpox occurred in the children’s ward of a local hospital. Six of the 23 children developed a fever following vaccination, and two of the six children also developed a mild rash. Study researchers reported uncertainty to whether the fever and rash were vaccine-related or related to a natural chickenpox infection modified by the administration of the vaccine. After vaccinating an additional 16 children with a diagnosis of kidney disease and reporting both the presence of antibodies considered protective against chickenpox and an absence of adverse reactions, researchers declared the vaccine safe for use in hospitalized children.

Additional clinical trials involving both healthy and hospitalized children were completed and in 1986, the Japanese government approved the vaccine for use in persons 12 months of age and older.

Meanwhile, in the United States, scientists working for Merck had isolated and attenuated a different chickenpox virus strain, the KMcC strain, but were unable to produce results similar to those observed after Oka strain vaccine administration. One study involving 369 healthy children found that those who received the KMcC chickenpox strain reacted significantly and “unacceptably” higher than those who were administered the OKA strain. In 1981, Merck licensed Japan’s Oka varicella virus strain and further attenuated the strain in MRC-5 cells – cells derived from lung tissue taken from a 14 week old male aborted fetus - prior to starting pre-licensure clinical trials in 1982.

Clinical trials of Varivax, Merck’s live, attenuated chickenpox virus vaccine, involved the use of different vaccine lots manufactured between 1982 and 1991. Manufacturing of the vaccine, however, changed several times, to increase the amount, stability and viability of the live virus and each vaccine lot contained a different amount of the live virus (plaque forming units or PFU), and varying ratios of live and dead viral antigens.

Only one double-blind, placebo-controlled study of the chickenpox vaccine was ever completed; however, the vaccine involved in this trial was not the formulation which eventually received FDA approval. This particular trial began in 1982 and involved 956 healthy children, 468 who received a chickenpox vaccine, and 446 who received a placebo. The experimental vaccine in this study contained 17,430 PFU while the placebo consisted of a lyophilized stabilizer containing at least 45 mg of neomycin.

Vaccine researchers reported that no cases of chickenpox occurred among vaccine recipients within the first year; however, 0.6 percent developed the illness in the second year. 8.5 percent of children in the placebo control group developed chickenpox within the first year. Vaccine recipients reported a significantly higher rate of swelling, pain and redness to the injection site in comparison to those who received the placebo. An additional clinical trial in 1982 involved the use of an experimental chickenpox vaccine containing 950 PFU but within two years, this vaccine had an efficacy of only 72 percent.

In 1984, Merck began another clinical trial involving 1,300 healthy participants who received experimental vaccine doses which contained anywhere from 2,460 to 14,000 PFU of attenuated chickenpox virus. Few study participants were actively followed, and researchers relied on parents to contact them to report breakthrough infections of chickenpox.

A 1987 study of an experimental vaccine which contained between 1,000 – 1,625 PFU of attenuated chickenpox virus involved 4,142 healthy children; however, researchers found that after 2 years, this formulation had an efficacy of only between 61 and 67 percent. The final pre-licensing clinical trial, which began in 1991, used vaccines with formulations of between 2,900 and 9,000 PFU. The vaccines used in this clinical trial were considered to be nearly identical to Varivax, the vaccine which eventually received FDA approval and is still currently in use in the United States. The trial involved only 1,164 participants and after a follow up period of 3 years, Merck reported that the vaccine was 93 percent effective against chickenpox illness.

The safety evaluation of Varivax chickenpox vaccine was completed by combining the safety data collected from all five pre-licensing clinical trials; however, only side effects which occurred at a rate of over one percent of all trial participants within 42 days of vaccine administration were included in the report. Of the 9,230 healthy vaccine recipients involved the trials, 62.5 percent experienced an upper respiratory illness and 40.4 percent reported a cough within 42 days of vaccination. Additional reported side effects included irritability/nervousness, sleep disturbance, fatigue, diarrhea, loss of appetite, and injection site complaints. The injection site complaints included pain, swelling, inflammation, itching and chickenpox-like rash.

Merck’s live chickenpox virus vaccine, Varivax, received FDA approval for use in March 1995 and each 0.5mL dose was reported to contain no less than 1,500 PFU of Merck/Oka varicella virus or no less than 1,350 PFU up to 30 minutes following reconstitution of the vaccine. Additional vaccine ingredients included monosodium-L-glutamate (MSG), sodium phosphate dibasic, potassium phosphate monobasic, potassium chloride, trace quantities of sodium phosphate monobasic, EDTA, neomycin, sucrose, hydrolyzed gelatin, sodium chloride, residual components of MRC-5 cells, and fetal bovine serum.

The FDA’s summary review of Varivax reported that the MRC-5 cells in Varivax vaccine contained unusual DNA. Prior to the vaccine’s licensure, the FDA expressed concerns that this residual DNA might potentially integrate into and change the cells of the vaccine recipient. However, after further evaluation, the FDA decided that the presence of approximately 2ug of cellular DNA in each vaccine dose would likely not cause harm and “that this anomaly did not pose a safety risk which exceeded the known benefit of the vaccine.”

The FDA summary report also noted the potential for vaccine recipients to transmit the vaccine virus to susceptible contacts and warned of the need for recently vaccinated persons to avoid contact with non-immune pregnant women and other susceptible high-risk individuals for several weeks post-vaccination.

The FDA also admitted that widespread use of the chickenpox vaccine could result in an increase in shingles infections. After chickenpox illness, the chickenpox virus will remain dormant in the sensory nerve ganglia of the body but can re-activate as shingles (herpes zoster) - a painful skin rash which often develops on one side of the body or face. Complications from shingles include balance or hearing issues, vision loss, and post herpetic neuralgia (PHN) - a severe and frequently long-lasting pain at the shingles rash site. Stating that scientific evidence suggested exposure to natural chickenpox decreased the risk of shingles, the FDA recommended careful monitoring of shingles rates post-vaccine licensure, to detect any changes.

In the spring of 1996, the CDC’s Advisory Committee on Immunization Practices (ACIP) voted to routinely recommend Merck’s live virus chickenpox vaccine, Varivax. In its formal recommendation published on July 12, 1996, ACIP recommended that all children without a prior history of chickenpox illness receive a single dose of the chickenpox vaccine beginning at 12 months of age. ACIP also recommended that all children 12 and under with no prior history of chickenpox illness receive a single dose of chickenpox vaccine. Persons 13 years and older with no prior history of illness were advised to receive two vaccine doses, administered 4-8 weeks apart.

The CDC acknowledged that recently vaccinated individuals could potentially transmit the infection to susceptible individuals, including immunocompromised household members; however, they reported that the benefit of vaccination would outweigh this potential risk. The vaccine, however, was not approved for use in persons with immune disorders such as HIV, AIDS, leukemia, lymphoma, blood disorders, lymphomas of any type, other malignant conditions which affected the lymphatic systems or bone marrow, pregnant women, nursing mothers, and persons with a family history of congenital immunodeficiency. Individuals with acute lymphoblastic leukemia (ALL) could, however, receive the vaccine free of charge from Merck as part of a research protocol, if they met certain predetermined criteria.

The cost-effectiveness analysis of implementing this recommendation was based on both direct medical costs and indirect costs associated with chickenpox illness. The analysis found that vaccinating all children with one dose of chickenpox vaccine could not be considered cost-effective if only medical costs were taken into consideration. When the indirect costs associated with loss of income (i.e. parent required to stay at home with a sick child) were included in the analysis, the CDC determined that routine chickenpox vaccination would be cost effective. The CDC declined to include any data on the potential costs associated with a rise in shingles cases among persons with a history of natural chickenpox illness or even among vaccinated children, and assumed that the implementation of the chickenpox vaccine program would not impact shingles rates.

In 1996, at the time of the CDC’s ACIP recommendation for routine administration of the newly licensed chickenpox vaccine, it was estimated that approximately 3.7 million cases of chickenpox occurred annually. However, as the illness was not nationally notifiable, the CDC acknowledged their surveillance data to be limited and ineffective to monitor the vaccine’s impact on chickenpox rates. In response, the CDC established three active chickenpox surveillance sites, in Antelope Valley, California, Travis County, Texas and West Philadelphia, PA. The CDC also recommended that state legislatures begin planning the implementation of chickenpox vaccine requirements for daycare, Head Start, and school entry, once the vaccine’s supply was considered adequate.

In February 1999, ACIP formally recommended that all states require proof of vaccination or immunity to chickenpox for both daycare and school entry, including middle school entry. The middle school requirement was made to reduce the risk of children reaching adulthood without immunity to chickenpox. ACIP also expanded chickenpox vaccine recommendations to include asymptomatic or mildly symptomatic HIV-positive children and children with impaired humoral immunity. Additionally, the chickenpox vaccine was recommended for use in susceptible individuals within 3 to 5 days of exposure to chickenpox, to prevent or reduce severity of the illness.

According to the CDC, by 2000, as chickenpox vaccination rates increased to between 74 and 84 percent of all 19 to 35-month olds within the active surveillance site communities (Antelope Valley, California, Travis County, Texas and West Philadelphia, PA), chickenpox infections decreased significantly.

The CDC, however, chose not to monitor shingles infections at any of the three active surveillance sites set up in 1995 to evaluate the impact of the chickenpox vaccine. Five years later, in 2000, shingles surveillance was finally added to California’s Antelope Valley Varicella Active Surveillance Project (AV-VASP), at a time when chickenpox infection rates had declined by 70 percent. By 2000, the number of reported shingles infections had already increased dramatically in adults 20 to 69 years of age. Further, children with a prior history of natural chickenpox infection were found to have shingles rates similar adults. Over a three-year period, between 2000 and 2002, the number of reported shingles cases increased by 56 percent (an 18 percent yearly increase).

Gary Goldman, Research and Epidemiology Analyst at AV-VASP, reported his shingles findings to multiple entities, including the CDC, site project investigators, Merck, and the FDA; however, the CDC chose to ignore his data and declined to publish any potential information suggesting that the chickenpox vaccine had resulted in an overwhelming increase in the number of shingles cases. Goldman resigned from AV-VASP on October 18, 2002, stating that “When research data concerning a vaccine used in human populations is being suppressed and/or misrepresented, this is very disturbing and goes against all scientific norms and compromises professional ethics.”

Goldman’s findings were not unique. In 2005, a CDC sponsored study was published on shingles rates in Massachusetts. This study found that between 1998 and 2003, as chickenpox vaccine rates increased and chickenpox infection rates decreased, the overall rate of shingles infections increased by 141 percent among all age groups. The incidence of shingles among adults between 25 and 44 years increased by 161 percent while rates among children and young adults aged one to 24 years increased by 152 percent.

As vaccination rates increased to approximately 90 percent, chickenpox infections among vaccinated individuals also increased, from two percent to 56 percent. Between 2001 and 2005, multiple chickenpox outbreaks among vaccinated school children were reported and vaccinated students were often found to be responsible for outbreaks. The vaccine was estimated by the CDC to be between 72 and 85 percent effective, however, one school reported that 40 percent of vaccinated school children in a particular classroom had developed chickenpox. While many cases of chickenpox were reported to be mild, up to 30 percent were not, and vaccinated children developed symptoms similar to those seen in children who experienced a natural chickenpox infection. By October of 2004, in response to the growing number of outbreaks among vaccinated school children, ACIP began discussions on the implementation of a second dose of chickenpox vaccine.

In September 2005, Merck received FDA approval for ProQuad (MMRV), a live virus vaccine containing measles, mumps, rubella, and varicella (chickenpox) antigens, for use in children 12 months to 12 years of age. ProQuad received approval without any formal clinical efficacy trials, as Merck was permitted by the FDA to submit data to show that the antibody response to ProQuad was not inferior to that of Varivax and MMRII administered simultaneously at separate injection sites.

According to the FDA’s clinical summary report to support ProQuad vaccine licensure, five vaccine trials involving over 1,600 children occurred in the 1980s and early 1990s. From these early clinical trials, Merck discovered that while the immune responses to measles, mumps, and rubella were similar to those seen after MMRII vaccination, the immune response to the chickenpox antigen was low and inadequate. In response, ProQuad was reformulated with a higher amount of chickenpox virus.

Five additional pre-licensing clinical trials were submitted to the FDA in support of ProQuad licensure, but no studies compared ProQuad to an inert placebo. Instead, clinical trials compared different formulations of ProQuad containing varying amounts of chickenpox virus to the administration of MMRII and Varivax vaccines given concomitantly; the safety and immunogenicity of one versus two doses of a ProQuad vaccine containing a high amount of chickenpox virus; the safety and tolerance of three different lots of ProQuad when compared with MMRII and Varivax vaccines administered concomitantly; the safety and immunogenicity of administering ProQuad in combination with Tripedia (Diphtheria, Tetanus, and whole cell Pertussis vaccine) and Comvax (combined Haemophilus Influenzae Type B and Hepatitis B vaccine) versus the administration of ProQuad followed by Tripedia and Comvax; and the immunogenicity of ProQuad when administered to healthy 4-6 year old children.

In pre-licensing clinical trials, 81.5 percent of children who received ProQuad and 79.6 percent of children who received MMRII and Varivax concomitantly reported at least one or more adverse events after vaccine administration. Further, 76.1 percent of children who received ProQuad and 72.3 percent of children who received MMRII and Varivax reported systemic adverse reactions which included fever, upper respiratory infection, measles-like rash, and chickenpox-like rash. Febrile seizures were also reported, however, per the FDA, the clinical trials “were not designed or powered to detect an increase in the frequency of this low frequency adverse reaction.”

On December 2, 2005, the CDC published a notice in regards to the licensing of Merck’s measles, mumps, rubella, and varicella (chickenpox) live virus vaccine, ProQuad (MMRV). In this notice, the CDC stated that the newly licensed ProQuad vaccine, approved for use in children 12 months to 12 years of age, could be used in lieu of separate doses of MMR and chickenpox vaccine, and that combination vaccines were preferential to separate doses of equivalent vaccine components. In 2005, all children were recommended to receive two doses of MMR vaccine, with the first dose at 12 to 15 months, and the second dose at 4 to 6 years. At this time, however, only a single dose of chickenpox vaccine was recommended, at 12 to 15 months of age. In this notice, the CDC stated that ProQuad could still be given to children previously vaccinated with Varivax vaccine if the MMR vaccine was not available, the potential benefits to the child outweighed the possible risk of receiving an additional dose of chickenpox vaccine, or in the event of a chickenpox outbreak, where an additional dose of chickenpox vaccine was recommended.

While acknowledging that little to no data existed to support the safety or effectiveness of administering ProQuad concomitantly with hepatitis A, influenza, DTaP, pneumococcal conjugate (Prevnar), or inactivated polio vaccines, the CDC recommended that ProQuad (MMRV) be administered simultaneously with any recommended vaccines.

In June 2006, in response to the significant rise of chickenpox illness among vaccinated individuals, ACIP voted to recommend a second dose of chickenpox vaccine for all children prior to school entry, at age 4-6 years. An additional dose of chickenpox vaccine was also recommended for all persons previously vaccinated with one vaccine dose. The CDC stated that adding a second dose of chickenpox vaccine would remain cost-effective but chose not to evaluate cost factors associated with the rise in shingles cases noted after the implementation of the chickenpox vaccination program and reported “that no consistent trends” indicate that the increase could be associated with the use of chickenpox vaccine.

The chickenpox vaccine supply became problematic for Merck in February 2007, due to manufacturing issues. In response, Merck reported that production of Varivax and its recently approved live virus shingles vaccine, Zostavax, would be prioritized over its ProQuad (MMRV) vaccine. Merck stated that it would be capable of meeting current demands for both Varivax and Zostavax, but by July 2007, their ProQuad (MMRV) vaccine would no longer be available.

In February 2008, data was presented at the CDC’s ACIP meeting in regards to a link between ProQuad (MMRV) and seizures. The Vaccine Safety Datalink (VSD), a collaborative project between several health care organizations and the CDC’s Immunization Safety Office (ISO), found that children between 12 and 23 months who received ProQuad vaccine were over twice as likely to suffer a seizure 5 to 12 days after vaccine administration when compared with children who received separate doses of MMRII and chickenpox vaccine. ACIP, however, chose not to issue a warning, but instead, revised its MMRV recommendation and stated that they did not "express a preference for use of MMRV vaccine over separate injections of equivalent component vaccines (i.e., MMR vaccine and varicella vaccine)."

While noting that ProQuad was not likely to become available before 2009, ACIP recommended the formation of a workgroup to evaluate the risk of seizures after MMRV vaccine administration.

Additional data presented by the workgroup confirmed an increased risk of seizures among children 12 to 23 months of age after MMRV administration when compared to those who received separate doses of MMRII and Varivax vaccines. In response, ACIP advised that for the first dose of measles, mumps, rubella, and varicella vaccine in children between the ages of 12 and 47 months, either MMRII and Varivax or MMRV could be used, unless a personal or family history of seizures existed. MMRV, however, was recommended over separate injections of MMRII and Varivax for the second dose, or for the first vaccine dose in children 48 months and older. In this recommendation, ACIP stated that “Given the balance of risks and benefits of a first dose of MMRV vaccine compared with a first dose of MMR vaccine and varicella vaccine, and the importance of individual values and preferences in weighing these risks and benefits, decisions should be made by providers and parents or caregivers on a case-by-case basis.”

In 2013, Gary Goldman, the Research and Epidemiology Analyst at California’s Antelope Valley Varicella Active Surveillance Project (AV-VASP) from 1995 to November 2002, published a review of the United States universal chickenpox vaccination program based on his experience at the AV-VASP site. Goldman reported that by 2000, chickenpox infection rates decreased by 70 percent at the AV-VASP site; however, by 2002, the vaccine’s efficacy was found to be less than 80 percent and cases of chickenpox illness were increasing among previously vaccinated individual. Further, between 2000 and 2001, shingles rates significantly increased among adults aged 20 to 69 years and children with a previous history of natural chickenpox illness had shingles rates that were similar to adult rates. From his findings, Goldman reported that shingles “morbidity costs have exceeded the cost savings from varicella-disease reductions.” He also stated that the current vaccination program had failed to eliminate chickenpox illness and had “proven extremely costly.”

In March 2023, the FDA approved both Varivax and ProQuad to be administered by intramuscular injection (IM), meaning injecting into muscle tissue. This approval is in addition to the previously approved subcutaneous (SC) injection route, meaning under the skin. Intramuscular injection was approved based on small clinical studies conducted by the manufacturer in 2005 showing the antibody responses to be similar between both routes of administration. Clinical trials also reported lower rates of injection site reactions among children who received vaccination by IM injection.

In their clinical review of the data, the FDA reported that allowing both the Varivax and ProQuad vaccines to be given by both IM and SC would recognize the importance of giving vaccine providers a choice on how to administer the vaccine and would align vaccination of these products with other vaccines. Additionally, the FDA noted that “current clinical recommendations concerning immunization practice do not require reimmunization when a vaccine indicated for the SC route is erroneously given IM (ACIP)”.

The CDC currently reports that one in three persons in the U.S. will develop shingles at some point in their lives, and the rate is increasing. They report, however, that they do not know why shingles rates are increasing but deny that the chickenpox vaccine is in anyway related to the increase. The CDC also reports that most cases of chickenpox occur among vaccinated persons but describe the illness as milder, with fewer than 50 lesions and lower rates of fever. They do, however, report that the modified clinical presentation of chickenpox among vaccinated individuals has resulted in diagnosing challenges for both parents and health care providers.

How effective is Chickenpox vaccine?

In 1996, when the CDC released its written report recommending the routine use of Merck’s newly licensed live chickenpox virus vaccine, Varivax, in young children 12 months of age and older, the vaccine was estimated to be between 70 and 90 percent effective at preventing chickenpox infections and 95 percent effective at preventing severe illness, for at least 7 to 10 years.

As vaccination rates increased, the number of chickenpox infections decreased; however, by 2001, rates began climbing again. Previously vaccinated children were developing chickenpox infections and frequently found to be responsible for classroom outbreaks. Outbreaks typically impacted younger elementary school children and in certain classrooms, up to 40 percent of vaccinated students developed the infection.

In 2002, a study published in the New England Journal of Medicine reported the chickenpox vaccine to be 44 percent effective against chickenpox infection and 86 percent effective against moderate or severe infection.Additional studies also reported on the failure of a single dose of chickenpox vaccine to prevent outbreaks, especially among school children.

In June 2006, ACIP voted to recommend that a booster dose of chickenpox vaccine be administered to all children, prior to school entry, between 4-6 years of age. Children under 12 who had previously received one dose of chickenpox vaccine were recommended to receive a second dose, with a minimal interval of at least three months. All persons over 12 years of age who had previously received one dose of chickenpox vaccine were also advised to receive a second dose, with a minimum interval of at least four weeks.

Exposure to natural chickenpox infection has been reported to delay or even eliminated the risk of shingles infection, an illness which is often more severe and potentially debilitating than chickenpox.European countries, such as the United Kingdom (UK) and the Netherlands, have chosen not to routinely recommend the chickenpox vaccine due to concerns that the reduction or elimination of chickenpox illness would result in a significant increase in shingles infections.

By the early 2000s, as chickenpox vaccine uptake increased, the incidence of shingles also rose significantly. One study found a 141 percent increase in the number of shingles cases over a five year period (1999-2003),while another found that shingles rates among children and adolescents increased by 63 percent between 2000 and 2006.

In 2006, when ACIP voted to recommend a booster dose of chickenpox vaccine, the CDC reported that the widespread use of the chickenpox vaccine had resulted in a significant decrease in chickenpox-associated hospitalizations and deaths. The CDC, however, chose not to report on the significant rise in rates of shingles which had occurred following the introduction of the chickenpox vaccine. Even prior to the introduction of the chickenpox vaccine, shingles related complications, hospitalizations, and deaths were reported to be 4-5 times higher than chickenpox morbidity and mortality.

A 2008 study reported that while chickenpox-associated hospitalizations and costs had decreased in the post-vaccine era, those decreases were significantly less than the increase in hospitalizations and costs associated with the rise in shingles cases.

The increase rate of shingles prompted Merck to introduce Zostavax, a live virus shingles vaccine in 2006, for use in adults 60 and older. In 2017, Shingrix, a recombinant, adjuvanted shingles vaccine manufactured by GlaxoSmithKline, received FDA approval for use in adults 50 years and older.

Since the two- dose chickenpox vaccine recommendation in 2006, chickenpox illness continues to be reported among vaccinated children, including those with a history of receiving two doses of the vaccine.

In 2006, an outbreak of chickenpox in Arkansas involving 84 students found that 25 (30 percent) students had received two doses of chickenpox vaccine and 53 (63 percent) had previously been vaccinated with a single vaccine dose. In 2011, two schools in Texas experienced an outbreak of chickenpox. In one school, one dose of chickenpox vaccine was found to be 80.9 percent effective, while two doses of the vaccine were noted to be 94.7 percent effective. At the second Texas school, vaccine effectiveness for one dose was 80.1 percent while 2-dose effectiveness was only at 84.2 percent.

In 2015, 9,455 cases of chickenpox were reported to the National Notifiable Disease Surveillance System (NNDSS) by the 40 reporting states. Of the 53 percent (4,982) of reported cases where vaccination status was known, 58 percent (2,900) of infections occurred among persons with a history of receiving at least one dose of chickenpox vaccine. Of those persons reporting a history of receiving at least one dose of the vaccine and who had information on the number of doses they received (2,207), 57 percent (1,261) reported receiving two doses.

A 2017 published study of approximately 10,000 Air Force recruits found that previously vaccinated recruits were 24 percent less likely to have the minimally required vaccine acquired antibody levels considered protective against chickenpox when compared with recruits reporting a history of natural chickenpox infection. Study authors concluded that antibody levels in young adults previously vaccinated with the chickenpox vaccine could not be considered acceptable to maintain herd immunity. Further, they also warned that “If vaccination in accordance with the current US VZV vaccination schedule is inadequate to maintain herd immunity, young adults not previously exposed to wild-type VZV may be at increased risk for varicella outbreaks.”

In addition to reports of vaccine failure, published studies have also found that the live virus chickenpox vaccine can cause vaccine strain chickenpox infection in both healthy and immune compromised recipients or among close contacts of a vaccinated individual.

A case report published in 2000 describes the case of two healthy brothers who were administered the chickenpox vaccine. Five months later, one of the boys developed shingles and then several weeks later the other boy developed a mild case of chickenpox. The chickenpox vaccine was found to be responsible for causing the vaccine strain of chickenpox that developed from exposure to vaccine strain shingles. The study authors cautioned that vaccinated individuals who develop shingles must still be considered contagious and noted that the risk of chickenpox transmission from a vaccinated person who develops shingles is unknown.

A similar case was reported in Japan, where a healthy 3-year-old girl developed shingles two years after receiving the chickenpox vaccine and her healthy brother developed vaccine strain chickenpox with a rash and fever shortly thereafter.

Chickenpox vaccine may also fail to protect immunocompromised individuals, including those with leukemia, and vaccinated persons with a history of asthma may also be at a higher risk of chickenpox illness.

Can chickenpox vaccine cause injury and/or death?

The Institute of Medicine (IOM) has acknowledged that there is individual susceptibility to vaccine reactions for genetic, biological and environmental reasons, but that vaccine providers cannot accurately predict prior to a vaccine’s administration who will suffer complications, injury or death from vaccination. However, a person who has previously had a serious reaction to a vaccination or is acutely or chronically ill should become informed about all potential risks associated with vaccination and discuss any concerns with a trusted health care professional before receiving a chickenpox vaccine or any other vaccine.

According to the CDC, possible side effects from the varicella (chickenpox) vaccine include:

Pain, swelling, and redness at the injection site
Fever
Seizures, often associated with fever
Full body rash
Pneumonia
Meningitis
Severe allergic reaction
Death

During the pre-licensing clinical trial of Merck’s Varivax (Varicella Virus Vaccine, Live) vaccine, reported adverse events included: injection site pain, redness, itching, swelling, rash, induration, bruising, and stiffness; fever; chickenpox-like rash at injection site; generalized chickenpox rash; upper respiratory infection; cough; irritability; nervousness; fatigue; sleep disturbances; loss of appetite; diarrhea; vomiting; inflammation of the ear; contact rash; diaper rash; other rash; heat rash; malaise; teething; headache; abdominal pain; muscle pain; chills; eye complaints; lymphadenopathy; nausea; lower respiratory infection; joint pain; stiff neck; dermatitis; itching; eczema; dry skin; constipation; allergic reaction; canker/cold sore; pneumonitis; and febrile seizures.

Serious complications reported by Merck since FDA licensure of Varivax have included:

Encephalitis
Stroke
Guillain-Barre Syndrome
Transverse Myelitis
Bell’s Palsy
Non-febrile seizures
Aseptic meningitis
Meningitis
Paresthesia
Dizziness
Ataxia
Anaphylaxis, including anaphylactic shock
Peripheral edema
Facial edema
Angioneurotic edema
Necrotizing retinitis in immunocompromised individuals
Thrombocytopenia
Idiopathic thrombocytopenic purpura (ITP)
Aplastic anemia
Vaccine strain chickenpox infection
Pneumonia
Pneumonitis
Pharyngitis
Henoch-Schönlein purpura
Erythema multiforme
Secondary bacterial infections of skin and soft tissue including cellulitis and impetigo
Shingles
Stevens-Johnson Syndrome

Meningitis or encephalitis caused by the vaccine-strain chickenpox virus have been reported in healthy individuals previously vaccinated with Varivax vaccine months to years after vaccination. Reported cases were commonly associated with a shingles rash.

In the comprehensive report evaluating scientific evidence, Adverse Effects of Vaccines: Evidence and Causality, published in 2012 by the Institute of Medicine (IOM), 15 reported vaccine adverse events following the varicella (chickenpox) virus vaccine were evaluated by a physician committee. These adverse events included disseminated vaccine strain virus with and without other organ involvement, vaccine strain viral reactivation (vaccine strain shingles) with and without other organ involvement, varicella encephalopathy, varicella seizures, acute disseminated encephalomyelitis, anaphylaxis, Guillain-Barre Syndrome, stroke, cerebellar ataxia, small fiber neuropathy, onset or exacerbation of arthropathy, transverse myelitis and thrombocytopenia.

The IOM committee concluded that in 5 out of 15 varicella (chickenpox) virus vaccine-related adverse events, the scientific evidence convincingly supported a causal relationship between the vaccine and the adverse event. These five adverse events included disseminated vaccine strain virus without organ involvement, disseminated vaccine strain virus with organ involvement, vaccine strain viral reactivation (vaccine strain shingles) without organ involvement, vaccine strain viral reactivation with organ involvement, and anaphylaxis. In the remaining 10 reported vaccine adverse events, the IOM committee concluded that there was inadequate evidence to support or reject a causal relationship between the chickenpox virus vaccine and the reported adverse event, primarily because there was either an absence of methodologically sound published studies or too few quality studies to make a determination.

In the past three decades, published studies have linked the chickenpox vaccine to serious adverse events in both children and adults. These adverse events include aplastic anemia, ocular complications, streptococcal toxic shock syndrome, skin rashes, thrombocytopenic purpura, stroke, pneumonia, Stevens - Johnson syndrome, and central nervous system disordersincluding meningitis, and encephalitis.

Adolescents between the ages of 11 and 17 are also at a higher risk of developing immune thrombocytopenic purpura (ITP) following chickenpox vaccination.

In 2013, the vaccine strain chickenpox virus was found to be responsible for the death of a 15-month-old vaccinated child. The young girl developed a chickenpox-like rash 20 days after receiving the chickenpox vaccine. She developed severe respiratory complications despite 2 months of anti-viral medications, and eventually died from sepsis and multi-organ failure.

Case studies have also found that severe complications can occur in persons with previously undiagnosed HIV infections who developed vaccine strain chickenpox after vaccination.While the live virus chickenpox vaccine is contraindicated in persons with a history of solid organ transplant, when administered, serious complications may occur.

Persons with a history of chickenpox vaccination may still be at risk for developing severe chickenpox infection, with complications which may include transverse myelitis, pneumonia, and meningitis. Children previously vaccinated with the chickenpox vaccine can also develop vaccine-strain shingles infectionswhich may result in serious complications.

In November 2014, the National Vaccine Information Center published a special report The Emerging Risks of Live Virus and Virus Vectored Vaccines: Vaccine Strain Virus Infection, Shedding and Transmission. This report reviewed the medical literature for evidence that live virus vaccine strain infection, shedding, and potential for transmission occurs, including chickenpox vaccine strain infection and shedding.

This report found that healthy children and adults can transmit vaccine strain chickenpox infection to other healthy children and adults but immune compromised persons were found to be at a special risk for contracting vaccine strain chickenpox infections and suffering complications. Published case studies in the medical literature have reported on vaccine strain chickenpox infections in solid organ transplant recipients, newborn infants, and individuals with cancer.

The Varivax chickenpox vaccine package insert states: “Post-marketing experience suggests that transmission of vaccine virus may occur rarely between healthy vaccinees who develop a varicella-like rash and healthy susceptible contacts. Transmission of vaccine virus from a mother who did not develop a varicella-like rash to her newborn infant has been reported. Due to the concern for transmission of vaccine virus, vaccine recipients should attempt to avoid whenever possible close association with susceptible high-risk individuals for up to six weeks following vaccination with VARIVAX.” High risk individuals include the immunocompromised; pregnant women who have never had varicella infection and their newborn infants; and premature babies born before 28 weeks gestation.

According to the CDC, possible side effects from the measles, mumps, rubella, and varicella (MMRV) vaccine include:

Pain, swelling, redness, and rash at the injection site
Fever
Swelling of the glands in the neck or cheeks
Seizures, often associated with fever
Full body rash
Low platelet count which may result in unusual bruising or bleeding
Encephalitis
Meningitis
Pneumonia
Severe allergic reaction
Death

The CDC also reports that there is a higher risk of seizures following the MMRV vaccine when compared with separate injections of MMR and varicella vaccines. This risk is significantly greater when the MMRV vaccine is administered as the first dose of the series.

Adverse events reported during the pre-licensure clinical trials of Merck’s ProQuad (MMRV) vaccine included: measles-like rash; chicken-pox rash; fever; injection site pain, tenderness, redness, swelling, ecchymosis, hemorrhage and rash; irritability; rash; viral exanthema; upper respiratory infection; diarrhea; vomiting; nasopharyngitis; eczema; and febrile seizure.

Serious complications reported by Merck in the ProQuad (MMRV) package insert during vaccine post-marketing surveillance have included:

measles;
atypical measles;
vaccine strain varicella;
varicella-like rash;
herpes zoster;
herpes simplex;
pneumonia and respiratory infection;
pneumonitis;
bronchitis;
epididymitis;
cellulitis;
skin infection;
subacute sclerosing panencephalitis;
aseptic meningitis;
thrombocytopenia;
aplastic anemia (anemia due to the bone marrow’s inability to produce platelets, red and white blood cells);
lymphadenitis (inflammation of the lymph nodes);
anaphylaxis including related symptoms of peripheral, angioneurotic and facial edema;
agitation;
ocular palsies;
necrotizing retinitis (inflammation of the eye);
nerve deafness;
optic and retrobulbar neuritis (inflammation of the optic nerve);
Bell’s palsy (sudden but temporary weakness of one half of the face);
cerebrovascular accident (stroke);
acute disseminated encephalomyelitis;
measles inclusion body encephalitis;
transverse myelitis;
encephalopathy;
Guillain-Barre syndrome;
syncope (fainting);
tremor;
dizziness;
paraesthesia;
febrile seizure;
afebrile seizures or convulsions;
polyneuropathy (dysfunction of numerous peripheral nerves of the body);
Stevens-Johnson syndrome;
Henoch-Schönlein purpura;
acute hemorrhagic edema of infancy;
erythema multiforme;
panniculitis;
arthritis;
death

A 2014 published study on the MMRV vaccine use in Canada found that the risk of febrile seizures following MMRV vaccination was double that of children receiving separate doses of MMR and varicella vaccines. Additionally, a 2015 meta-analysis found a two-fold increase in febrile seizures between 5 and 12 days following MMRV vaccination in children between the ages of 10 and 24 months.

MMRV vaccine contains albumin, a human blood derivative, and as a result, a theoretical risk of contamination with Creutzfeldt-Jakob disease (CJD) exists. Merck states that no cases of transmission of CJD or other viral diseases have been identified and virus pools, cells, bovine serum, and human albumin used in vaccine manufacturing are all tested to assure the final product is free of potentially harmful agents.

As of the March 29, 2024 data release, there have been 105,487 reports of varicella vaccine (Varicella, MMRV) reactions, hospitalizations, injuries and deaths following varicella vaccinations made to the federal Vaccine Adverse Events Reporting System (VAERS). This includes 245 related deaths, 3,895 hospitalizations, and 853 related disabilities. However, the number of vaccine-related injuries and deaths reported to VAERS may not reflect the true number of serious health problems that occur after chickenpox vaccination.

Even though the National Childhood Vaccine Injury Act of 1986 legally required pediatricians and other vaccine providers to report serious health problems following vaccination to federal health agencies (VAERS), many doctors and other medical workers giving vaccines to children and adults fail to report vaccine-related health problem to VAERS. There is evidence that only between 1 and 10 percent of serious health problems which occur after use of prescription drugs or vaccines in the U.S. are ever reported to federal health officials, who are responsible for regulating the safety of drugs and vaccines and issue national vaccine policy recommendations.

As of April 1, 2024, there have been 195 claims filed in the federal Vaccine Injury Compensation Program (VICP) for injuries and deaths following chickenpox vaccination (Varicella, MMRV), including 13 deaths and 182 serious injuries. Of that number, the U.S. Court of Claims administering the VICP has compensated 103 children and adults, who have filed for varicella vaccine injury.

Who is at highest risk for complications from Chickenpox vaccine?

There is a gap in medical knowledge in terms of doctors being able to predict who will have an adverse reaction to chickenpox vaccination, and who will not.

The package insert of Merck’s live, attenuated chickenpox vaccine, Varivax, states that immunocompromised individuals who receive the vaccine may develop an extensive rash associated with the vaccine and/or disseminated chickenpox disease. Vaccination with chickenpox vaccine is contraindicated in persons with immunosuppression due to this risk. Persons with a family history of hereditary or congenital immunodeficiency may also be at higher risk of complications from vaccination and should not receive the vaccine until immune function has been determined. Children taking aspirin or aspirin containing products who receive Varivax vaccine may be at risk for the development of Reye syndrome, a rare illness which affects the liver, blood, and brain, and may lead to coma and brain death.

Immunocompromised persons, pregnant women, newborn infants born to mothers without immunity to chickenpox, and all infants born prior to 28 weeks gestation may be at risk of developing chickenpox infection through close contact with someone who has received Varivax vaccination. Chickenpox, including vaccine-strain virus, in these high-risk populations may result in complications.

Merck’s ProQuad (MMRV) vaccine product insert states that children between the ages of 12 and 23 months with no history of vaccination or wild-type infection with measles, mumps, rubella, and varicella have a higher risk of fever and febrile seizure between 5- and 12-days following vaccination with MMRV in comparison to children who receive separate doses of MMRII and Varicella vaccine. Children with a personal or family history of convulsion, a personal history of cerebral illness, or a medical condition where stress from fever should be avoided may also be at a higher risk of developing complications following MMRV vaccination.

Individuals most at risk for complications from MMRV vaccine include persons with both primary and acquired immunodeficiency such as AIDS, dysgammaglobulinemic and hypogammaglobulinemic states, and cellular immune deficiencies. Pneumonitis, measles inclusion body encephalitis, and death have also occurred as a result of being inadvertently vaccinated with a measles-containing vaccine. Reports of disseminated chickenpox vaccine virus infections in children with underlying immunodeficiency disorders who were inadvertently vaccinated with a chickenpox-containing vaccine have also been documented.

Who should not get Chickenpox vaccine?

Contraindications to receiving Varivax chickenpox vaccine as documented by Merck in their vaccine package insert include:

Persons who have experienced a severe allergic reaction or anaphylaxis to any Varivax vaccine component, including gelatin and neomycin;

Persons who are immunodeficient or immunosuppressed. This includes individuals with AIDS or clinical symptoms of infection with HIV, lymphoma, leukemia, primary or acquired immunodeficiency states or other malignant neoplasms that affect the lymphatic system or bone marrow;
Persons receiving corticosteroid or other immunosuppressive therapies;
Febrile illness or active untreated tuberculosis;
Pregnant women. Women who receive Varivax should wait at least 3 months following vaccination before getting pregnant;
Persons with a family history of hereditary or congenital immunodeficiency should not be vaccinated with Varivax until the immune competence of the recipient has been determined.

Transmission of the vaccine virus has been documented between healthy persons who have received the vaccine and developed a chickenpox-like rash and healthy susceptible contacts. The vaccine virus has also been transmitted between a mother who did not develop a chickenpox-like rash, and her newborn child. As a result, persons who receive Varivax should avoid close contact with susceptible high-risk individuals for up to six weeks post-vaccination, to reduce the risk of transmission. These susceptible individuals include:

Persons who are immunocompromised;
Pregnant women without lab evidence or documented history of chickenpox;
Newborn infants whose mothers have no lab evidence or documented history of chickenpox;
All premature infants born at less than 28 weeks gestation.

The chickenpox vaccine should not be given until at least five months have passed since the administration of plasma, blood transfusions or immunoglobulins. Further, immunoglobulins should not be given for at least two months following Varivax vaccine unless the use of immunoglobulins outweighs the benefits of vaccination.

Aspirin and aspirin-containing products should not be given to infants and children between 12 months and 17 years of age for at least six weeks following Varivax due to an association between aspirin therapy and Reye syndrome.

Varivax is approved for use in individuals 12 months of age and older. Varivax is not approved for use in children under the age of 12 months.

Contraindications to receiving ProQuad (MMRV) vaccine as documented by Merck in their vaccine package insert include:

A severe allergic reaction or anaphylaxis to any MMRV vaccine component, including gelatin and neomycin;

Febrile illness or active untreated tuberculosis;
Acquired or primary immunodeficiency status or use of immunosuppressive therapies. Vaccination with MMRV should be delayed for 3 months following the administration of human immune globulin, blood, or plasma;
A family history of hereditary or congenital immunodeficiency;
Pregnancy;

Leukemia, lymphoma, blood dyscrasias and other malignant neoplasms affecting the lymphatic systems or bone marrow.

Merck’s ProQuad product insert warns of a higher incidence of fever and febrile seizures in children between the ages of 12- and 23-months following administration of MMRV in comparison to children who receive separate doses of MMR and varicella vaccines. Caution is advised when administering MMRV vaccine in children with a history of seizures, cerebral injury, or any other medical condition where stress from fever should be avoided.

Both live measles and mumps vaccine are manufactured in chick embryo cell culture. Extreme caution should be taken when vaccinating individuals with a history of anaphylaxis or immediate hypersensitivity to eggs. Merck advises that a careful evaluation of the risks and benefits should be completed when vaccination is being considered in this population.

Merck’s MMRV vaccine package insert reports that transmission of varicella vaccine virus may occur between vaccine recipients and susceptible contacts, including both healthy and high-risk individuals, resulting disseminated disease. As a result, Merck cautions that vaccine recipients should attempt to avoid close contact with high-risk individuals. This population includes pregnant women who lack a positive history of illness or vaccination and their newborn infants, any infants born prior to 28 weeks gestation, and any immunocompromised individuals.

Merck also advises that a careful evaluation of the risk and benefits of vaccination with MMRV be completed in children with thrombocytopenia or history of the blood disorder, as no clinical data on the development or exacerbation of this condition exists. Thrombocytopenia has been reported following vaccination with MMRII, measles vaccine, varicella vaccine and again following an additional dose of both measles and MMRII vaccines.

The safety or efficacy of MMRV vaccine in HIV-positive children is unknown.

Children who receive MMRV vaccine should avoid the use of salicylate (aspirin) or salicylate-containing products for 6 weeks following vaccination due to the association of Reye Syndrome with aspirin use and wild-type varicella disease.

MMRV vaccine is approved for use in children 12 months to 12 years of age. Children under the age of 12 months or older than 12 years of age should not receive MMRV vaccine.

What questions should I ask my doctor about the Chickenpox vaccine?

NVIC’s If You Vaccinate, Ask 8! Webpage downloadable brochure suggests asking eight questions before you make a vaccination decision for yourself, or for your child. If you review these questions before your appointment, you will be better prepared to ask your doctor questions. Also make sure that the nurse or doctor gives you the relevant Vaccine Information Statement (VIS) for the vaccine or vaccines you are considering well ahead of time to allow you to review it before you or your child gets vaccinated. Copies of VIS for each vaccine are also available on the CDC's website and there is a link to the VIS for varicella (chickenpox) and MMRV vaccines on NVIC's “Quick Facts” page.

It is also a good idea to read the vaccine manufacturer product insert that can be obtained from your doctor or public health clinic because federal law requires drug companies marketing vaccines to include certain kinds of vaccine benefit, risk and use information in product information inserts that may not be available in other published information. Chickenpox vaccine package inserts are located on the chickenpox disease and vaccine quick facts page.

Other questions that may be useful to discuss with your doctor before getting the chickenpox (Varicella/MMRV) vaccine are:

If other vaccines in addition to Varicella/MMRV vaccine are scheduled for my child at this office visit, am I allowed to modify the schedule so fewer vaccines are given at once?
What should I do if my child has a high fever or appears very ill after vaccination?
What other kinds of reaction symptoms should I call to report after Varicella/MMRV vaccination?
If the Varicella/MMRV vaccine doesn’t protect my child, do I have any other options for preventing chickenpox infection?

Under the National Childhood Vaccine Injury Act of 1986, doctors and all vaccine providers are legally required to give you vaccine benefit and risk information before vaccination; record serious health problems following vaccination in the permanent medical record; keep a permanent record of all vaccines given, including the manufacturer’s name and lot number; and report serious health problems, injuries and deaths that follow vaccination to VAERS.

Remember, if you choose to vaccinate, always keep a written record of exactly which shots/vaccines you or your child have received, including the manufacturer’s name and vaccine lot number. Write down and describe in detail any serious health problems that develop after vaccination, and keep vaccination records in a file you can access easily.

It also is important to be able to recognize a vaccine reaction and seek immediate medical attention if the reaction appears serious, as well as know how to make a vaccine reaction report to federal health officials at the Vaccine Adverse Reporting System (VAERS). NVIC’s Report Vaccine Reactions—It’s the Law webpage can help you file a vaccine reaction report yourself to VAERS if your doctor fails or refuses to make a report.

NVIC Press Releases, Statements & Commentaries Related to Chickenpox

NVIC Press Releases

NVIC Challenges VAERS Data of Chickenpox Vaccine’s Adverse Reactions - September 13, 2000

NVIC Statements & Commentaries

Chicken Pox Vaccine Associated with Shingles Epidemic - Sept 2005
Chickenpox Vaccine Shipped Out - The Vaccine Reaction, May 1995 Additional Information

The Vaccine Reaction

Mercola J Is the Chickenpox Vaccine Creating a Shingles Epidemic? The Vaccine Reaction Dec. 20, 2018
Raines K Chickenpox Vaccine May Increase Shingles Risk The Vaccine Reaction Apr. 26, 2016
Raines K, Fisher BL CDC Accused of Manipulating Shingles Data The Vaccine Reaction Aug. 19, 2018

Chickenpox Disease and Vaccine Quick Facts

Chickenpox

Chickenpox (Varicella) is a highly-contagious infection that is generally mild in most children;
The virus is transmitted through direct contact with, or by inhaling particles from chickenpox blisters. It may also be spread through respiratory secretions of a person infected with the virus;
Chickenpox generally begins between 10 and 21 days after exposure to the virus and the illness typically lasts between 5 and 10 days. In adults, initial chickenpox symptoms can include headache, fever, loss of appetite, and fatigue. These symptoms usually occur 1 to 2 days prior to the onset of a rash; however, in children, the rash is often the first sign of infection. When the chickenpox rash erupts, it will frequently begin with raised red or pink bumps that are followed by small fluid-filled blisters (vesicles) that form from the initial bumps. These vesicles then break open and eventually crust and scab over. The rash usually starts on the head, progresses to the trunk, and finally to the arms and legs. The rash may also be present in the eyes, throat, and genitals;
Complications from chickenpox are rare in healthy children and may occur more frequently in persons over age 15. Complications from chickenpox include pneumonia, central nervous system manifestations, bacterial infections of a skin lesion, and Reye syndrome. Persons with underlying immune disorders may be at a greater risk for complications from chickenpox;
Recovery from chickenpox confers long lasting natural immunity and immunocompetent individuals rarely experience a second attack. Re-exposure to chickenpox has been found to boost immunity and reduce the risk of shingles infection in older children and adults.

Chickenpox Vaccine

There are currently two varicella (chickenpox) vaccines used in the United States: Varivax, a live chickenpox virus vaccine and ProQuad, a combination measles-mumps-rubella-varicella (MMRV) live virus vaccine, both produced and distributed by Merck. The CDC recommends children receive a first dose of chickenpox vaccine between age 12 and 15 months, and a second dose between age 4 and 6;
Mild side effects, such as redness, rash, or pain at the injection site, as well as fever, have been reported following chickenpox vaccination. More serious side effects of chickenpox vaccine include meningitis, pneumonia, seizures, full body rash, allergic reaction, and death. Mild side effects following MMRV vaccination include rash, redness, or pain at the injection site, fever and swelling of the glands in the neck or cheeks. More serious side effects of MMRV vaccine may include loss of hearing, meningitis, pneumonia, full body rash, seizure, coma, brain damage, severe allergic reaction, and death;
Chickenpox vaccine is reported to be between 80 and 85 percent effective at preventing chickenpox and more than 95 percent effective at preventing severe illness. The widespread use of chickenpox vaccine in the U.S. has substantially increased the rate of shingles infections in adults, as a natural boost of immunity from exposure to chickenpox in the environment is no longer occurring;
As of April 1, 2024, there have been 195 claims filed in the federal Vaccine Injury Compensation Program (VICP) for injuries and deaths following chickenpox vaccination, including 13 deaths and 182 serious injuries;

Using the MedAlerts search engine, as of March 29, 2024, there have been 105,487 reports of chickenpox vaccine reactions, hospitalizations, injuries and deaths following chickenpox vaccinations made to the federal Vaccine Adverse Events Reporting System (VAERS); this includes 245 related deaths, 3,895 hospitalizations, and 853 related disabilities. Nearly 52 percent of varicella vaccine-related adverse events occurred in children under six years of age.

Food & Drug Administration (FDA)

Varicella Virus Vaccine Live Product Insert & Licensing Information
Measles, Mumps, Rubella and Varicella Virus Vaccine Live Product Insert & Licensing Information

Centers for Disease Control (CDC)

Search for Vaccine Reactions

NVIC hosts MedAlerts, a powerful VAERS database search engine. MedAlerts examines symptoms, reactions, vaccines, dates, places, and more.

Reporting a Vaccine Reaction

Since 1982, the NVIC has operated a Vaccine Reaction Registry, which has served as a watchdog on VAERS. Reporting vaccine reactions to VAERS is the law. If your doctor will not report a reaction, you have the right to report a suspected vaccine reaction to VAERS.

Vaccine Reaction Symptoms

Our Ask 8, If You Vaccinate webpage contains vaccine reaction symptoms and more.

Additional Bibliography of References

Medical Literature

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Goldman GS The US Universal Varicella Vaccination Program: CDC Censorship of Adverse Public Health Consequences. Ann Clin Pathol. 2018 Mar; 6(2): 1133
Marchetti S, Guzzetta G, Flem E et al. Modeling the impact of combined vaccination programs against varicella and herpes zoster in Norway. Vaccine. 2018 Feb 14;36(8):1116-1125
Duncan JR, Witkop CT, Webber BJ, Costello AA Varicella seroepidemiology in United States air force recruits: A retrospective cohort study comparing immunogenicity of varicella vaccination and natural infection. Vaccine. 2017 Apr 25;35(18):2351-2357
Van Lier A, Lugnér A, Opstelten W et al. Distribution of Health Effects and Cost-effectiveness of Varicella Vaccination are Shaped by the Impact on Herpes Zoster. EBioMedicine. 2015 Aug 8;2(10):1494-9.
Goldman GS, King PG Vaccination to prevent varicella: Goldman and King's response to Myers' interpretation of Varicella Active Surveillance Project data. Hum Exp Toxicol. 2014 Aug; 33(8): 886–893. 168573500
Leung J, Siegel S, Jones JF et al Fatal varicella due to the vaccine-strain varicella-zoster virus Hum Vaccin Immunother. 2014 Jan 1; 10(1): 146–149.
Goldman GS, King PG. Review of the United States universal varicella vaccination program: Herpes zoster incidence rates, cost-effectiveness, and vaccine efficacy based primarily on the Antelope Valley Varicella Active Surveillance Project data. Vaccine. 2013 Mar 25;31(13):1680-94.
Kluthe M, Herrera A, Blanca H et al. Neonatal vaccine-strain varicella-zoster virus infection 22 days after maternal postpartum vaccination. Pediatr Infect Dis J. 2012 Sep;31(9):977-9.
O'Leary ST, Glanz JM, McClure DL et al. The risk of immune thrombocytopenic purpura after vaccination in children and adolescents. Pediatrics. 2012 Feb;129(2):248-55
Patel MS, Gebremariam A, Davis MM. Herpes zoster-related hospitalizations and expenditures before and after introduction of the varicella vaccine in the United States. Infect Control Hosp Epidemiol. 2008 Dec;29(12):1157-63
Lopez AS, Guris D, Zimmerman L et al. One dose of varicella vaccine does not prevent school outbreaks: is it time for a second dose? Pediatrics. 2006 Jun;117(6):e1070-7.
Goldman GS Universal varicella vaccination: efficacy trends and effect on herpes zoster. Int J Toxicol. 2005 Jul-Aug; 24(4):205-13
Yih WK, Brooks DR, Lett SM, et al. The incidence of varicella and herpes zoster in Massachusetts as measured by the Behavioral Risk Factor Surveillance System (BRFSS) during a period of increasing varicella vaccine coverage, 1998-2003. BMC Public Health. 2005 Jun 16; 5:68.
Welsby PD Chickenpox, chickenpox vaccination, and shingles Postgrad Med J. 2006 May; 82(967): 351–352.
Lee BR, Feaver SL, Miller CA et al. An elementary school outbreak of varicella attributed to vaccine failure: policy implications. J Infect Dis. 2004 Aug 1;190(3):477-83
Galil K, Lee B, Strine T et al. Outbreak of varicella at a day-care center despite vaccination. N Engl J Med. 2002 Dec 12; 347(24):1909-15.
Brisson M, Gay NJ, Edmunds WJ et al. Exposure to varicella boosts immunity to herpes-zoster: implications for mass vaccination against chickenpox. Vaccine. 2002 Jun 7;20(19-20):2500-7.
Edmunds WJ, Brisson M. The effect of vaccination on the epidemiology of varicella zoster virus. J Infect. 2002 May; 44(4):211-9.