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Varicella Zoster (Chickenpox) Disease and Vaccine

Quick Facts


chicken pox
  • Chickenpox is highly contagious but mild for most children
  • Chickenpox symptoms include low grade fever and skin lesions with intense itching lasting two to three weeks
  • Chickenpox complications, such as bacterial infection of skin lesions (cellulitis), brain inflammation and pneumonia, are rare in children but more common in adults
  • Most children and adults, who have complications from chickenpox, have compromised immune systems or other underlying health problems
  • Recovery from chickenpox confers long lasting natural immunity in populations, where the disease is circulating and older children and adults are asymptomatically boosted by periodic contact with younger children with chickenpox

Chickenpox Vaccine

  • There are two live virus vaccines for chickenpox licensed in the U.S.: Varivax and ProQuad (MMRV) manufactured by Merck;
  • The CDC recommends children get a chickenpox shot at 12 months old and a booster dose between 4 and 6 years old;
  • Reported complications from chickenpox vaccine include shock, seizures, brain inflammation (encephalitis), thrombocytopenia (blood disorder), Guillian Barre syndrome, death and infection with vaccine strain chickenpox or transmission of vaccine strain chickenpox to others;
  • Chickenpox vaccine effectiveness is reported to be 44 percent for any form of the disease and 86 percent for moderate to severe disease;
  • Mass use of chickenpox vaccine by children in the U.S. has removed natural boosting of immunity in the population, which was protective against shingles, and now adults are experiencing a shingles epidemic;
  • In 2006, the CDC recommended a booster dose of chickenpox vaccine for all children and a shingles vaccine was licensed and recommended for all adults over age 60.
  • As of September 1, 2015, there had been 122 claims filed in the federal Vaccine Injury Compensation Program (VICP) for injuries and deaths following chickenpox or varicella vaccination, including 8 deaths and 114 serious injuries.
  • Using the MedAlerts search engine, as of July 31, 2018 there had been 3,936 serious adverse events reported to the Vaccine Adverse Events Reporting System (VAERS) in connection with chickenpox and varicella-containing vaccines since 1990. Over half of those serious chickenpox vaccine-related adverse events occurring in children six years old and under. Of these chickenpox-vaccine related adverse event reports to VAERS, 192 were deaths, with over 70% of the deaths occurring in children under six years of age.

Food & Drug Administration (FDA)

Centers for Disease Control (CDC)

Vaccine Reaction Symptoms & Ingredients

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

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.

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.

What is Chickenpox?

Chickenpox is caused by the varicella zoster virus, which is a member of the herpes virus family and is associated with herpes zoster (shingles). Chickenpox is highly contagious but for the vast majority of children in developed countries like the U.S. it is a mild disease characterized by small round lesions on the skin that cause intense itching and last from two to three weeks.

Half of all varicella zoster cases occur in children between the ages of 5 and 9. It has been estimated that, before the chickenpox vaccine was introduced in the U.S. in 1995, only 10 percent of Americans over the age of 15 had never had chickenpox.

Recovery from chickenpox usually gives lifelong immunity in populations, where the disease is circulating and older children and adults are asymptomatically boosted by periodic contact with younger children, who have chickenpox. 

Can Chickenpox Cause Injury and Death?

Yes. 3.7 million cases of varicella zoster were estimated to occur in the US annually in the early 1990s before the chickenpox vaccine was licensed in 1995, although only a fraction were reported to the government. Data from 1992 showed that about 158,000 cases of chickenpox were reported, including about 100 deaths. More than half of the deaths were in adults because chickenpox is more serious in adults than in children.

Up to 20 percent of adults who get chickenpox can develop severe complications such as pneumonia. Other rare complications from chickenpox include serious bacterial infection of the lesions (cellulitis) and brain inflammation, which is reported in less than one percent of children who get chickenpox.

Most children and adults, who develop severe complications and are injured or die from chickenpox disease, have compromised immune systems or other underlying health problems.

What is Chickenpox Vaccine?

Currently there are two live virus vaccines for chickenpox licensed in the U.S.: Varivax and ProQuad (MMRV) and both are manufactured by Merck. Varivax contains only varicella vaccine and ProQuad is a 4 in 1 combo shot containing varicella, measles, mumps and rubella vaccines. A CDC vaccine safety study found that children aged 12-23 months were twice as likely to experience febrile seizures with ProQuad compared to administering MMR and Varivax separately.

The vaccine product insert for VariVax vaccine states the following:

"VARIVAX* [Varicella Virus Vaccine Live] is a preparation of the Oka/Merck strain of live, attenuated varicella virus. The virus was initially obtained from a child with wild-type varicella, then 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). Further passage of the virus for varicella vaccine was performed at Merck Research Laboratories (MRL) in human diploid cell cultures (MRC-5) that were free of adventitious agents. This live, attenuated varicella vaccine is a lyophilized preparation containing sucrose, phosphate, glutamate, processed gelatin, and urea as stabilizers. 

Refrigerator-stable VARIVAX, when reconstituted as directed, is a sterile preparation for subcutaneous administration. Each 0.5 mL dose contains the following: a minimum of 1350 plaque forming units (PFU) of Oka/Merck varicella virus when reconstituted and stored at room temperature for 30 minutes, approximately 18 mg of sucrose, 8.9 mg hydrolyzed gelatin, 3.6 mg of urea, 2.3 mg of sodium chloride, 0.36 mg of monosodium L-glutamate, 0.33 mg of sodium phosphate dibasic, 57 mcg of potassium phosphate monobasic, 57 mcg of potassium chloride. The product also contains residual components of MRC-5 cells including DNA and protein and trace quantities of neomycin and bovine calf serum from MRC-5 culture media. The product contains no preservative."

How Effective is Chickenpox Vaccine?

All vaccines only provide temporary immunity. Only recovery from natural chickenpox disease will provide lifelong immunity in populations with circulating varicella zoster, where adults are asymptomatically boosted by coming into contact with children, who have chickenpox. 

When the chickenpox vaccine was licensed for public use in 1995, the Food and Drug Administration (FDA) estimated that it was 70 to 90 percent effective in preventing disease. A Centers for Disease Control (CDC) study in 2002 reported that "the effectiveness of the vaccine was 44 percent against disease of any severity and 86 percent against moderate or severe disease."

Another study in 2002 confirmed that adults exposed to children with natural chickenpox disease were protected from developing shingles later in life and that mass vaccination against chickenpox is likely to cause an epidemic of shingles affecting more than 50 percent of American children and adults over age 10.

After “breakthrough” cases of chickenpox continued to occur in children given a chickenpox shot at 12 months of age, in 2006 the CDC recommended a booster dose of varicella zoster vaccine for all children 4-6 years old.

Responding to continuing concern that mass vaccination of children against chickenpox is causing an epidemic of shingles in older adults, in 2006, Merck’s live virus shingles vaccine was licensed and recommended by the CDC for all adults over age 60. The shingles vaccine is basically an adult booster dose of varicella zoster vaccine.

Can Chickenpox Vaccine Cause Injury and Death?

Yes. Between March 1995 and July 1998, the federal Vaccine Adverse Events Reporting System (VAERS) received 6, 574 reports of health problems after chickenpox vaccination. That translates into 67.5 adverse events per 100,000 doses of vaccine or one in 1,481 vaccinations. About four percent of cases (about 1 in 33,000 doses) were serious including shock, encephalitis, thrombocytopenia (blood disorder) and 14 deaths.

The VAERS data analysis led to the addition of 17 adverse events to the manufacturer's product label after the vaccine was licensed in 1995, including secondary bacterial infections (cellulitis); secondary transmission of vaccine strain virus infection to close contacts; transverse myelitis; and Guillain Barre syndrome; and herpes zoster (shingles). There have been documented cases of transmission of vaccine strain virus from a vaccinated child to household contacts, including a pregnant woman.

A CDC vaccine safety study found that children aged 12-23 months were twice as likely to experience febrile seizures with the 4 in 1 combination shot, ProQuad, which contains varicella zoster, measles mumps and rubella vaccines, compared to administering MMR vaccine and Varivax separately.  

Should Chickenpox Vaccine Be Mandated?

NVIC did not support the addition of chickenpox vaccine to the mandatory childhood vaccine schedule after it was licensed in 1995 and recommended for universal use in all children. The vast majority of children recover from chickenpox disease and do not suffer complications. They are left with a qualitatively superior immunity to the disease.

The chickenpox vaccine only gives temporary immunity and leaves older children and adults vulnerable to chickenpox later in life when complications can be much more serious. Mass use of the chickenpox vaccine by children has eliminated the opportunity for natural asymptomatic boosting of immunity in adults and left adults vulnerable to shingles later in life.

Vaccine reaction reports to VAERS suggest that the vaccine is more reactive than it was thought to be before licensure. By 2011, there had been nearly 50,000 reports of adverse events, including 115 deaths, associated with varicella zoster vaccine.

There are too many outstanding questions about the true adverse event profile of this live virus vaccine. Parents should have the right to make an informed, voluntary decision about whether or not to give their children chickenpox vaccine.

NVIC's Chickenpox (Varicella Zoster) Commentaries and Video Collection

NVIC Chickenpox Video Playlist

View the collection of video resources within the player below for more information on chickenpox and the chickenpox vaccine.

To view the entire video collection, click the hamburger menu in the upper left corner of the video player above. This will expand a full list of videos. You may also open the video player in full screen mode for optimal display.

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