Low Varicella Vaccine Effectiveness Identified at Day Care Center

CHICAGO (Reuters Health) Dec 19 - New study findings indicate that, at least among one group of children, the varicella vaccine is much less effective than previously reported.

Dr. Jane Seward, from the US Centers for Disease Control and Prevention in Atlanta, and colleagues reported Tuesday on their investigation of a recent outbreak of chickenpox at a New Hampshire day care center. They presented their findings here at the 41st Annual Interscience Conference on Antimicrobial Agents and Chemotherapy.

The outbreak in 23 children began with a child who had been vaccinated, contradicting the belief that such "breakthrough" cases are not contagious, Dr. Seward noted. The child, a 4-year-old, was confirmed not to have developed varicella infection from the vaccine, but probably developed it after exposure to a sibling with shingles.

Previous findings indicate that the vaccine's effectiveness ranges from 71% to 91%. In the current study, however, the effectiveness that was only about 40%. "Ours is the first study that has shown anything significantly below that level," co-author Dr. B. R. Lee of the CDC told Reuters Health.

Dr. Seward and Dr. Lee say they cannot yet explain why the vaccine was ineffective in this group of children. "We'd like to really understand what factors came together to produce it," Dr. Seward added. "We're not dismissing it."