Updated: April 26, 2007
Before vaccine became available, “chickenpox parties” were considered a way to get a child protected from serious chickenpox at an age when the infection is ordinarily less severe. Since varicella disease (a.k.a. chickenpox) is generally thought to provide lifelong immunity, prior to an available vaccine, ‘chickenpox parties’ were a strategy to reduce the risk of acquiring chickenpox as an adolescent or adult when the disease is much more severe.
However, after the varicella vaccine was licensed in 1995, children could obtain immunity against varicella without the risks of natural infection and its potential complications. While chickenpox is generally milder in children, severe disease with serious complications does occur. Indeed, most serious disease occurs in previously well children.
Although it is possible for vaccinated children to develop chickenpox after exposure to chickenpox (or to shingles), the illness is much milder (fewer pox, shorter illness) in those who have been vaccinated than in those who haven’t been vaccinated1 2.
The typical case of chickenpox begins 10 to 14 days after exposure and is often associated with fever. The rash is very itchy: there may be 10 to 1500 blisters but the usual child will have about 300 lesions.
One of the most common complications of chickenpox is that the blister can become infected with bacteria; this happens to about one in 20 children. One of the most dreaded complications of chickenpox is invasive Group A streptococcal infection which may be fatal. Since the vaccine was licensed this type of infection has decreased as a complication of chickenpox3.
Children with chickenpox who are treated with aspirin are at risk of a serious complication called Reye’s Syndrome with brain swelling and liver failure; this complication decreased before vaccine was introduced when aspirin was no longer recommended for treating fever in children. Another complication of chickenpox is encephalitis (brain inflammation with abnormal gait and clumsiness that may last for a number of days (this occurs in about 1 in every four thousand cases of chickenpox).
Children with immune problems, such as those being treated for leukemia, may develop a very severe form of chickenpox. They are best protected by not being exposed to chickenpox; that is, by their brothers, sisters and classmates being immune.
Chickenpox vaccine’s effectiveness to protect against all chickenpox symptoms decreases after the first year but it is still protective against ‘full blown’ chickenpox after 8 years (it was licensed in the US in 1995). Thus, children who have been immunized who later develop chickenpox after exposure tend to have mild episodes (usually without fever and the lesions are often just bumps, although sometimes a few blisters form) because the vaccine is still protective against full blown chickenpox.
Because mild chickenpox does occur in some vaccinated children that are exposed to chickenpox, researchers have asked what the ideal immunization strategy for chickenpox is; whether there should be a second dose of varicella vaccine for all children; whether varicella vaccination should be given after 15 months of age instead of after 12 months.4 5
Children who develop chickenpox despite having received the vaccine are less contagious than unvaccinated children who develop chickenpox, largely as a consequence of having fewer lesions. A recent study found that even under the circumstances of intense exposure in a household, chickenpox vaccine was about 80% effective in preventing all disease and reduced the number of persons with large numbers of lesions.6
Varicella vaccine recommendations are regularly updated as new information becomes available to assure optimal safety and protection.