Medical Health Encyclopedia

There is currently intense debate over the long-term protection of the vaccine. Such controversy is stimulated by the incidence of breakthrough infections after vaccination. It should be noted, however, that evidence is showing improvements in quality of life and better survival rates since the introduction of the vaccine. Any negative studies to date on long-term effectiveness simply raise the question of the need for booster or higher doses--not the elimination of the vaccine altogether.

Long-Term Protection in Vaccinated Children. Most studies suggest that the vaccine is not wholly effective in up to 30% of vaccinated children. However, they also report if chickenpox occurs, more than 95% of the cases are mild. It is also usually less contagious. In such people, the infection appears to be caused by a wild virus, not a reactivation of the vaccine. (Of concern was a 2002 study of a day care center reporting a much higher rate--56%--of break-through infection-- with only 86% of cases being mild. The implications of this study are unclear.) The longer the interval since vaccination occurs, the higher the risk for a breakthrough infection.

This does not necessarily mean, however, that children who are vaccinated eventually lose total immunity. A breakthrough infection is often due to issues with the primary vaccine (improper storage, low potency, the duration between the chickenpox and MMR vaccines being less than month) or the child''s history (having asthma, being less than 14 months at the time of vaccination). Nevertheless, there is also some evidence that either having the vaccination or even having chickenpox itself is not as protective against a later infection as experts have thought.

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Long-Term Protection in Vaccinated Adults. The protective effects for adults are even less clear. An encouraging 2002 study of adults vaccinated between 1979 and 1999 reported that 9% developed chickenpox months to years after their last vaccination. The length of time since the vaccination did not seem to affect whether the adults would catch chickenpox or not. (Nearly half of those had been exposed to the disease in their homes.) In all cases, infection was mild, with none of the serious complications of adult chickenpox.