Yale researchers recommend a double dose of the chicken pox vaccine to prevent illness in children.

According to a study to appear in the Feb. 1 issue of the Journal of Infectious Diseases, a second dose of the vaccine lessens the risk of getting chicken pox by 95 percent. The study confirms a 2006 policy of the Centers for Disease Control and Prevention that recommended a second dose.

In 1995, the CDC recommended one dose for children aged 1 to 13, a policy that led to a significant reduction in chicken pox cases, preventing the sickness in 86 percent of children. In 2006, the CDC issued a new recommendation, this time for two doses.

Eugene D. Shapiro, M.D., professor in the Department of Pediatrics at Yale and fellow researchers at Yale and Columbia University, examined the data of 71 children aged 4 and over who had gotten chicken pox. Of these, 93 percent had received only one dose of the vaccine, and 7 percent had received no dose at all. None had received two doses.

"The findings confirm that, at least in the short term, the policy of routinely administering two rather than one dose of varicella vaccine is sensible," Shapiro said in a press release. "Other countries that are routinely immunizing children with varicella vaccine may consider changing to a two-dose regimen."

It is not possible to predict who will have a mild case of chickenpox and who will have a serious or even deadly case of disease. Even with uncomplicated cases, children with chickenpox miss an average of 5-6 days of school, and parents or other caregivers miss 3-4 days of work to care for sick children. Compared with children, adults are at increased risk of complications related to chickenpox.

Vaccination is the best way to prevent infection with varicella—the virus that causes chickenpox—both in an individual and in the community. Widespread vaccination also reduces the risk of exposure to infection for persons at risk for serious disease who cannot be vaccinated because of illness or other conditions. The vaccine is safe and effective, and should be used to prevent as many cases as possible.

Who should be vaccinated

- All healthy children 12 months through 12 years of age should have two doses of chickenpox vaccine, administered at least 3 months apart. Children who have evidence of immunity to varicella do not need the vaccine.

- People 13 years of age and older who do not have evidence of immunity should get two doses of the vaccine 4 to 8 weeks apart.

Chickenpox vaccination is especially important for certain groups of susceptible adults.