Dose Titration Study of Live Attenuated Varicella Vaccine in Healthy Children

To approximate the effect of prolonged storage on safety and immunogenicity, healthy children were given a single dose of the currently marketed live attenuated varicella vaccine (3625 pfu) or of a partially heat-inactivated vaccine (1125 or 439 pfu), The 3 doses had similar antigen content (attenuated plus inactive virus particles). The vaccine was well tolerated. No significant differences in adverse reactions were observed. Although the seroconversion rates were excellent at each dose (?:98%), the higher doses resulted in significantlygreater geometric mean antibody titers at 6 weeks (10.5 and 10.6 ELISA U/mL) compared with the 439 pfu dose (5.7 ELISA U/mL),P ::0:; .01. One year after immunization, differences in antibodies were similar to the 6-week postimmunization results. Results indicate that until the date of expiry, the vaccine's immunogenicity will be preserved and there will be no clinically important changes in type or frequency of adverse events.