Immunogenicity and safety of different schedules of 2-dose varicella vaccination in China

We evaluated the safety and immunogenicity of different time intervals for a second dose of varicella vaccine in children in Zhejiang Province, China. Participants had all received a first dose of varicella vaccine and were assigned to 4 groups according to age (2-7 years). A second dose of live attenuated varicella vaccine was administered 1 month, 1 year, 3 years, or 5 years after the first. A serology assay was conducted and fluorescent-antibody-to-membrane-antigen test performed to measure the antibody titers against varicella before and approximately 30 days after the second dose. Of 1,078 participants, most tolerated the second dose well. Age at first dose did not affect the response to vaccination. Geometric mean titers (GMTs) significantly differed between group 1 and all other groups, both before and after the second vaccination. The GMT for group 1 was higher than those for the other 3 groups prior to the second vaccination (GMT = 20.52, 14.68, 12.49, 12.29, respectively, p < 0.001 for all), while the opposite was true after the second vaccination (GMT = 51.14, 83.37, 85.01, 81.83, respectively, p < 0.001 for all). There was no significant difference in seropositive rate among the 4 groups prior to the second vaccination (p = 0.093), and these rates were all 100% after the second vaccination. The vaccine was well tolerated in healthy children, regardless of the timing of the second dose. GMTs showed a particularly high boost after the second dose when the interval between doses was more than 1 year.