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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.1  The varicella virus is found only in humans and outbreaks generally occur between March and May in the United States.2

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.3 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.4

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.5 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.6 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 1 to 4 millimeters in diameter.7

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 currently is limited at this time.8 A person with breakthrough chickenpox is still contagious and can spread the illness on to others.9  

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.10

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.11 Infants born to mothers infected with chickenpox between 5 days prior to and 2 days post-delivery, premature infants, pregnant women, and persons with immunosuppressive conditions are considered to be at highest risk of developing complications.12

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 1 and 4 years were found to have the highest rates of chickenpox infections and were followed closely by children between 5 and 9 years. Only 7 percent of chickenpox infections occurred in adults.13  Chickenpox was removed from the list of nationally reportable diseases in 1981 but returned to the list in 2003.14 Chickenpox- related death have been nationally notifiable since 199915 and in 2017, 2 chickenpox- associated deaths were reported in the United States.16

Recovery from chickenpox confers long lasting natural immunity and immunocompetent individuals rarely experience a second attack.17 Re-exposure to the chickenpox virus will boost a person’s immune system and decrease their risk of shingles infection.18

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.

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1 CDC Varicella – Varicella Zoster Virus Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015

2 CDC Varicella – Epidemiology Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.

3 CDC Chickenpox (Varicella) For Healthcare Professionals – Transmission Dec. 31, 2018

4 CDC Varicella – Clinical Features Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.

5 Mayo Clinic Chickenpox – Symptoms Feb. 27, 2019

6 CDC Varicella – Clinical Features Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.

7 Ibid

8 CDC Chickenpox (Varicella) For Healthcare Professionals Clinical Features Dec. 31, 2018

9 CDC Prevention of Varicella Recommendations of the Advisory Committee on Immunization Practices (ACIP) MMWR Jun. 22, 2007; 56(RR04);1-40

10 Ibid

11 CDC Chickenpox (Varicella) – Complications. Dec. 31, 2018

12 CDC Chickenpox (Varicella) - People at High Risk for Severe Varicella Dec. 31, 2018

13 CDC Varicella - Secular Trends in the United States Epidemiology and Prevention of Vaccine-Preventable Diseases (The Pink Book). 13th ed. 2015.

14 CDC National Notifiable Diseases Surveillance System (NNDSS) Varicella/Chickenpox No Date

15 Lopez AS, Marin M Strategies for the Control and Investigation of Varicella Outbreaks Manual, 2008 National Center for Immunization and Respiratory Diseases (NCIRD), Division of Viral Diseases (DVD) Dec. 31, 2018

16 CDC National Notifiable Infectious Diseases and Conditions: United States TABLE 2o. Reported cases of notifiable diseases, by region and reporting area - - United States and U.S. territories, 2017 Atlanta, GA. CDC Division of Health Informatics and Surveillance, 2018.

17 Bechtel K Pediatric Chickenpox Medscape Nov. 30, 2018

18 NHS Why aren't children in the UK vaccinated against chickenpox? Sep. 20, 2016

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