Chickenpox (Varicella) Vaccine Safety

Chickenpox and How to Protect Against It

Chickenpox, or varicella, is a very contagious disease caused by the varicella-zoster virus (VZV). It causes a blister-like rash, itching, tiredness, and fever. Chickenpox can be serious, especially in babies, adults, and people with weakened immune systems. It spreads easily from infected people to others who have never had chickenpox or never received the chickenpox vaccine. Chickenpox virus spreads in the air through coughing or sneezing. It can also be spread by touching or breathing in the virus particles that come from chickenpox blisters.

You can protect against chickenpox with safe, effective vaccination.

Chickenpox Vaccine Side Effects

The chickenpox vaccine is very safe, and it is effective at preventing chickenpox. Vaccines, like any medicine, can have side effects. Most people who get chickenpox vaccine do not have any problems with it. The vaccine is usually given in two doses.  Side effects are more likely after the first dose than after the second.

Serious side effects after the chickenpox vaccine are extremely rare. The few that have been reported after vaccination include severe rash, infections of the lungs or liver, meningitis, seizures, pneumonia, or general severe infection with the virus strain from the vaccine. Some children who had these serious side effects after vaccination had weakened immune systems before they were vaccinated, but they had not been diagnosed by a doctor at the time of vaccination.

People who get chickenpox vaccines can spread the vaccine-strain varicella-zoster-virus to others. However, this happens very rarely.

Pregnant women, people who are moderately or severely ill at the time the shot is scheduled, and people allergic to any vaccine component should not get chickenpox vaccine. For more information, see Contraindications and Precautions for Varicella Vaccination.

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Available Chickenpox Vaccines

There are two chickenpox vaccines approved for use in the United States, one of which is combined with vaccines for other diseases:

• Varivax: The Food and Drug Administration (FDA) approved this vaccine in 1995 for use in people 1 year of age and older.
• ProQuad [PDF -425 KB]: FDA approved this vaccine in 2005 for use in children ages 1 through 12 years of age. It protects against measles, mumps, rubella, and varicella (MMRV).

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How CDC Monitors Chickenpox Vaccine Safety

CDC and FDA continuously monitor the safety of vaccines after they are approved.  If a problem is found with a vaccine, CDC and FDA will inform health officials, health care providers, and the public.

CDC uses three systems to monitor vaccine safety:

• The Vaccine Adverse Event Reporting System (VAERS): an early warning system that helps CDC and FDA monitor problems following vaccination.  Anyone can report possible vaccine side effects to VAERS.
• The Vaccine Safety Datalink (VSD): a collaboration between CDC and nine health care organizations which allows ongoing monitoring and proactive searches of vaccine-related data.
• The Clinical Immunization Safety Assessment (CISA) Project: a partnership between CDC and several medical centers that conducts clinical research on vaccine-associated health risks.

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A Closer Look at the Chickenpox Vaccine Safety Data

• The chickenpox vaccine has been shown to be safe and well tolerated. The most commonly reported side effects after vaccination are soreness or swelling where the shot was given, fever, and mild rash.  Very rare side effects include seizures and pneumonia.
• Before the FDA licensed the vaccine, studies were done to determine the safety of 2 doses of the vaccine. In children 12 months through 12 years old:
  • 1 of 5 children had side effects, such as soreness, swelling, and redness, within 3 days of getting the first dose compared with 1 of 4 children after the second dose
  • 7 of 100 children had fever after the first dose compared with 4 of 100 children after the second dose
  • 3 of 100 children had chickenpox-like rash after the first dose compared with 1 of 100 children after the second dose
• In 2008, a CDC-FDA report analyzed VAERS data on patients who reported side effects after getting chickenpox vaccine during May 1995 through December 2005. The vaccine manufacturer Merck distributed 50 million doses of chickenpox vaccine during this time. The report found that the vast majority of people had no or very mild side effects, such as rash and soreness, with the vaccine. Serious side effects linked to the vaccine were extremely rare.
• Rarely, serious adverse events after chickenpox vaccination have been reported. These include thrombocytopenia (low platelet count), acute cerebellar ataxia (brain injury that leads to balance problems), and acute hemiparesis (paralysis on part the body). It is not known if these side effects were caused by the vaccine. Lab testing was either not done or did not confirm if the problems were caused by vaccine.
• Although pregnant women should not get the chickenpox vaccine, there are women who may get the vaccine by mistake. In 1995, Merck, Inc., in collaboration with CDC, established a Pregnancy Registry to monitor the fetal and pregnancy outcomes of women who inadvertently received chickenpox vaccine 3 months before or at any time during pregnancy. After 17 years of monitoring, no cases of congenital chickenpox syndrome or increased risk for other birth defects have been identified.

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More Resources

• Chickenpox Vaccine Information Statement
• Chickenpox Vaccine: Who Should Not Get Vaccinated
• Measles, Mumps, Rubella, and Varicella (MMRV) Vaccine Safety
• Chickenpox Vaccination: What Everyone Should Know
• Information for Parents: Chickenpox and the Vaccine (Shot) to Prevent It
• Chickenpox Fact Sheet [PDF – 300 KB]
• Information for Healthcare Providers: Varicella Vaccination
• CDC’s Chickenpox  Disease Website

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Related Scientific Articles

Chaves SS, Haber P, Walton K, Wise RP, Izurieta HS, et al. Safety of varicella vaccine after licensure in the United States: Experience from reports to the Vaccine Adverse Event Reporting System, 1995-2005. J Infect Dis. 2008 Mar 1;197 Suppl 2:S170-7.
 

Klein NP, Yih WK, Marin M, Jumaan AO, Seward JF, et al. Update: Recommendations from the Advisory Committee on Immunization Practices (ACIP) Regarding Administration of Combination MMRV Vaccine. MMWR. 2008 March 14;57(10):258-60.
 

Marin M, Broder KR, Temte JL, Snider DE, Seward JF. Use of Combination Measles, Mumps, Rubella, and Varicella Vaccine—Recommendations of the Advisory Committee on Immunization Practices. MMWR. 2010 May 7; 59(RR03):1-12.
 

Marin M, Willis ED, Marko A, Rasmussen SA, Bialek SR, et al. Closure of varicella-zoster virus-containing vaccines pregnancy registry – United States, 2013. MMWR. 2014 Aug 22;63(33):732-3.
 

Wise RP, Salive ME, Braun MM, Mootrey GT, Seward JF, et al. Postlicensure safety surveillance for varicella vaccine. JAMA. 2000 Sep 13;284(10):1271-9.
 

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