When the new vaccine against varicella infection, or chickenpox, was approved by the U.S. Food and Drug Administration in 1995, many wondered how effective it would be. According to the largest study to date, Yale researchers have found that it prevents the disease 85 percent of the time, and even in those who develop the disease, symptoms are almost always very mild. If most children get the vaccine, the investigators believe that it could one day wipe out chickenpox altogether.

The study, published in the March 29 issue of The New England Journal of Medicine, surveyed 591 children at pediatric practices in New Haven. The study showed that the vaccine worked as well as predicted and was especially effective—97 percent—at eliminating severe cases of the disease, which formerly caused 11,000 hospitalizations and some 100 deaths each year.

According to study director Marietta Vazquez, M.D., a postdoctoral fellow in pediatric infectious diseases, “The effectiveness of the vaccine as it is used in actual practice is excellent, at least in the short term. If its use is fairly widespread, the potential is there for complete eradication of the disease.” She notes that some questions remain about what will happen as the prevalence of the disease wanes. “Exposure to chickenpox tends to boost immunity against chickenpox.”

She said that it may be too soon to assess the long-term effectiveness of the vaccine. Vazquez and her colleagues plan to continue their study to determine whether the vaccine will continue to work as well over time. For now, she said, “I recommend that every healthy child a year or older, as well as adults with no previous history of chickenpox, receive the vaccine.”