Long-term immunogenicity and immune persistence of live attenuated and inactivated hepatitis a vaccines: a report on additional observations from a phase IV study.

Both live attenuated (HA-L) and inactivated (HA-I) hepatitis A vaccine were licensed for routine use in China. Although phase 1, 2 and 3 clinical studies of both vaccines have been completed, further systematic evaluation of their immunogenicity and immunological persistence under phase 4 clinical studies in a wide range of conditions and involving large populations is necessary. A phase IV clinical trial (NCT02601040) was performed in 9000 participants over 18 months of age. Geometric mean concentrations (GMCs) and seroconversion rates (SRs) were compared at five time points during 3 years for 1800 individuals among them. The SRs of HA-L and HA-I were 98.08% (95% CI 95.59%-99.38%) and 99.64% (95% CI 98.93%-100.00%) respectively 28 days after administration of the first dose, and remained at 97.07% (95% CI 94.31%-98.73%) or above and 96.73% (95% CI 94.07%-98.42%) or above respectively during the following 3 years. The GMCs for both the HA-L and HA-I groups showed that both vaccines elicited high anti-HAV titres, considerably more than the threshold of protection needed against HAV infection in humans, and these titres were sustained. Hence, both HA-I and HA-L vaccines could provide an excellent long-term protective effect, and supported the routine use of both vaccines.