Varicella vaccine much more effective with 2 doses

Two doses of varicella vaccine significantly reduce patients' risk of getting chickenpox, according to a new study.

The study, published in the Feb. 1 issue of The Journal of Infectious Diseases, found that children who received two doses of the vaccine were 95% less likely to develop the condition than those who got a single dose (link).

The Centers for Disease Control and Prevention began recommending vaccinating children against varicella in 1995. The CDC added a second dose to the recommendation in June 2006 for children who never got chickenpox.

Physicians should administer the first dose between ages 12 months to 15 months, according to the CDC. The second dose should be given to children ages 4 to 6.

"When the vaccine was first approved as a one-dose regimen, it was pretty effective. ... But over a longer period of time, it didn't prevent" cases of breakthrough varicella, said lead study author Eugene D. Shapiro, MD. Breakthrough varicella often is less severe than the traditional infection, but it can be transmitted to people who are not vaccinated against the disease.

"The evidence is that two doses are highly effective in preventing chickenpox and, hopefully, this will prevent outbreaks and lower the risk of these children getting shingles when they grow older," said Dr. Shapiro, professor of pediatrics and epidemiology and deputy director of investigative medicine at Yale School of Medicine in Connecticut.

Before a varicella vaccine was licensed in 1995, the disease caused about 11,000 hospitalizations and 100 deaths in the U.S. each year, the CDC said. Between 2000 and 2006, when one dose was recommended, there was an average of 3,498 varicella-related hospitalizations a year, according to a study published online Jan. 3 in Pediatrics (link).

Administering a second dose probably will lead to additional declines in varicella incidence and hospitalization, the Pediatrics study said.