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The Chicken Pox Vaccine

How the Chicken Pox Vaccine Works and Who Should Get It


Updated May 15, 2014

Since wide-spread vaccination began in the mid-1990's, the incidence of chicken pox has decreased dramatically. Varivax is the live-virus vaccine that produces persistent immunity against chicken pox. The virus used for the vaccine is known as the Oka strain. It is an attenuated strain meaning it is much weaker than naturally occurring varicella. This weaker virus infects the cells and replicates in the bloodstream causing the immune system to develop antibodies to fight it off. In most cases this infection is subclinical, meaning it does not produce symptoms. If a vaccinated person gets chicken pox, the disease is mild 95% of the time. The length of time these antibodies stay effective is controversial, but it appears that vaccination does confer long-lasting immunity.

Side Effects of the Chicken Pox Vaccine
The side effects of the chicken pox vaccine are usually mild and include:

  • Low-grade fever
  • Mild discomfort at the vaccination site
  • A limited rash at the vaccination site (about 3-5 lesions)

Who Should Get the Chicken Pox Vaccine
The chicken pox vaccine is recommended for all children between the ages of 18 months and adolescence who have not yet had chicken pox. Studies have also shown that the vaccine can prevent chicken pox or reduce the severity of the illness if it is given with 3-5 days of exposure to an infected person. Some experts recommend that any healthy adult who does not have a known history of chicken pox infection be vaccinated. Some studies also show that the chicken pox vaccine may prevent or reduce the severity of shingles in adults over 55 years of age who had a childhood bout of chicken pox.

Who Should NOT Get the Chicken Pox Vaccine
Because the chicken pox vaccine contains a live virus it is not recommended for the people with the following:

  • Pregnant women
  • History of previous chicken pox infection
  • Compromised immune system
  • Exposure to the varicella virus less than 21 days previously
  • Allergy to neomycin
  • Transfusion of IgG or other blood products within the past 5 months
  • Administration of aspirin or aspirin-containing products within the past 6 weeks

Chicken Pox Vaccine Controversies
Certain aspects of vaccination for chicken pox are either unknown or are under study. The two controversial aspects are vaccination of infants and the need for booster shots. Currently there are no recommendations or studies on infants who develop chicken pox during the first year of life. In older patients booster shots may be needed to maintain adequate levels of antibodies to prevent shingles.

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