The chickenpox vaccine doesn’t protect only the inoculated child; it also protects infants who are too young to be vaccinated but for whom the disease is especially dangerous. This protection conferred on non-immunized people by a high rate of vaccination in the area is called “herd immunity” (or community immunity).
A recent study, just published in the journal Pediatrics, assessed trends in chickenpox (varicella) infections and mortality since the vaccine for this illness has moved into widespread use. The authors report an impressive decline in the number of cases of varicella since the U.S. vaccination program was initiated in 1995, with fewer hospitalizations and deaths from this disease. But what was especially surprising was the significant reduction in varicella incidence among infants who were still too young to receive the vaccine: Rates among infants under 12 months decreased by 90 percent, from over 15 cases per 1,000 in 1995 to less than two per 1,000 in 2008.
What was responsible for the remarkable decline in the incidence of chicken pox among unvaccinated infants? As fewer children are infected with varicella since the vaccination program was implemented, there are fewer people to spread the chickenpox virus to very young infants, who are especially susceptible to the disease. As ACSH’s Dr. Gilbert Ross explains, “This is what community, or herd, immunity is all about. Much like the flu vaccination, which has been shown to protect older family members from potentially lethal influenza, the news about the varicella vaccine’s efficacy among the very young is one more reason to make sure children get immunized on schedule.”
ACSH’s Dr. Josh Bloom points out that chickenpox is a member of the herpes family of viruses, which are known to be very dangerous to newborns. “All the more reason to get your older kids vaccinated,” he says.
