Long-term antibody persistence after vaccination with a 2-dose Havrix™ (inactivated hepatitis A vaccine): 20 years of observed data, and long-term model-based predictions.

Antibody persistence in two cohorts of adults, who received inactivated hepatitis A (HAV) vaccine (1440El.U; Havrix ™; GSK Vaccines) according to a 0–6 or 0–12 month schedule in 1992–1993, has been measured annually. After 20 years, >97% of the subjects in both studies were seropositive for anti-HAV antibodies. Geometric mean concentrations in the according-to-protocol cohorts were 312 mIU/ml in 34/36 subjects vaccinated initially at 0–6 months ( NCT00289757 ) and 317 mIU/ml in 85/86 subjects vaccinated at 0–12 months ( NCT00291876 ). Over the whole follow-up period, seven subjects (2 + 5, respectively) lost circulating anti-HAV antibodies but mounted a strong response after HAV booster administration (1440El.U). Mathematical modelling, which was applied to assess true persistence at Year 20 (accounting for drop-outs and missing data), and to predict longer-term persistence confirmed previous estimates that seropositive anti-HAV levels would persist in ≥95% vaccinees at Year 30 and ≥90% at Year 40. ClinicalTrials.Gov number: NCT00289757 / NCT00291876 [ABSTRACT FROM AUTHOR]