Loading...
Although varicella incidence has decreased dramatically in the U.S. since the introduction of universal varicella immunization in 1995, disease outbreaks have continued to occur in highly vaccinated populations. Might vaccine-induced immunity diminish with time? To find out, researchers from the CDC and the Los Angeles County Department of Health Services examined varicella surveillance data from Antelope Valley, California (population, 350,000).
From 1995 through 2004, 11,356 cases of varicella were reported in this population, including 1080 cases (9.5%) with onset >42 days after vaccination. During the decade of observation, annual varicella incidence decreased by 85%, and the proportion of cases in immunized children increased from 1% to…