By Matt Leingang
The Cincinnati Enquirer

A new study might spark debate among pediatricians and parents about the effectiveness of the chickenpox vaccine and when it should be given to children.

Researchers at Yale Medical School say the effectiveness of the vaccine fades significantly in the first year after vaccination. And the vaccine also doesn't appear to be as effective in children younger than 15 months.

Pediatricians typically give the vaccine to healthy children beginning at 12 months, which is the recommendation of the American Academy of Pediatrics.

So should the vaccination age be pushed from 12 months to 15 months? The study, which appears in a February issue of the Journal of the American Medical Association, stops short of saying that.

"My job as a researcher is to present data.," said Dr. Marietta Vazquez, a pediatric infectious disease specialist at Yale and the study's lead author.

Vazquez said she still thinks parents should children vaccinated against chickenpox when they are 12 months old. Delaying the vaccination could put children at risk for exposure to the disease, she said.

Vazquez said she was surprised at the study's findings.

Researchers tracked 339 children who had chickenpox and compared them with 678 children who never had the disease from March 1997 to June 2003.

Overall, the vaccine was 87 percent effective for children who received it. But a year after the vaccine was given, its effectiveness waned, slipping from an average of 97 percent to 84 percent in years 2 through 8.

For children who had the shot at 15 months or older, the protection reached 99 percent in the first year. But in children vaccinated before 15 months, immunity in the first year was 73 percent.

Dr. Matthew Hardin, an assistant professor of internal medicine and pediatrics at University Hospital, has started to delay giving the vaccine until 15 months. "I certainly discuss it with families," Hardin said. "Theoretically, you could say that it puts the child at risk for exposure between 12 and 15 months, but studies like this one show that the vaccine is a little more effective if you wait."

E-mail mleingang@enquirer.com