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Vaccine Chokes Chickenpox

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March 29, 2001 -- It's one thing for a drug or vaccine to prove itself effective in a clinical trial, where conditions are controlled and participants carefully selected. The more important question is how will the product perform in real life? When it comes to the chickenpox vaccine, Yale University School of Medicine researchers say the answer is ... just fine.

The research team reviewed community use of the chickenpox vaccine over three years and found it outright prevented the disease in 85% of vaccinated children. In those children who got chickenpox, the vaccine kept the disease from advancing beyond a mild stage. The study results appear in the March 29 issue of The New England Journal of Medicine.

Study author Eugene Shapiro, MD, from the pediatrics department at Yale, says the study shows the vaccine is highly effective. "It's 85% effective overall, but it is 99% effective against severe chickenpox," he says. "So it works very well."

Shapiro and colleagues surveyed various health centers in New Haven, Conn., during a three-year period, looking specifically for children with "potential" chickenpox -- keeping in mind than many cases of chickenpox were diagnosed by phone. They compared the children with chickenpox to a group of children without chickenpox. Some of the children in both groups had been vaccinated against disease.

The researchers identified about 200 children who tested positive for the disease.

Of the kids with confirmed chickenpox, less than 25% had been vaccinated compared with 61% in the noninfected group. Those who had been vaccinated and still got the disease were nearly twice as likely to suffer a mild case of chickenpox (86%) than unvaccinated kids (48%). Moderate to severe disease only struck 14% of the vaccinated kids, but more than 50% of those unvaccinated.

Though the study did not look at the vaccine's possible side effects, Shapiro tells WebMD that his experience with it has been good. The study does note, however, that a small number of those vaccinated (about 7%) developed a drug-induced rash, which cleared up in a few days.

Baby boomers, who grew up during a time when there was no chickenpox vaccine, might remember the disease as little more than an inconvenience. But Shapiro says not everybody experiences it the same way. "Before the days of the vaccine, about 100 patients a year died from chickenpox or complications of chickenpox, and 9,000 were hospitalized," he says.

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