Efficacy of high-titer live attenuated varicella vaccine in healthy young children

The efficacy of a high-titer, reformulated varicella vaccine was studied in 513 10- tb 30-month-old children. Vaccinees were randomly allocated to 5 groups to receive one of two lots of an original high-titer vaccine, one of two lots of a partially heat-inactivated vaccine, or placebo. Both vaccines were well tolerated, Seroconversion was detected in 100% and 99% of children immunized with the high- and low-titer vaccines, respectively, Sixty-five cases of serologically confirmed varicella-like disease were discovered during follow-up (mean, 29.3 months): 5 in the high-titer vaccine group, 19 in the low-titer vaccine group, and 41 in the placebo group (P less than or equal to.005 for each difference), Thus, the protective efficacy of live attenuated varicella vaccine is dependent on vaccine titer. High-titer varicella vaccine induces excellent protection in healthy young children.