Antibody response to inactivated hepatitis A vaccine

Abstract

We examined the seroconversion rate and level of hepatitis A virus antibodies induced by inactivated hepatitis A vaccine. Inactivated hepatitis A vaccine was administered intramuscularly to 127 healthy antibody negative subjects at doses of either 0.5 and 1.0 μg two or three times. Convalescent sera from 21 adults with acute hepatitis A were also assayed. Serum antibody titers were measured by enzyme-linked immunosorbent assay. Seroconversion occurred in all 127 subjects (43 children, 84 adults). Acquired antibody levels in children in the early stage were higher than those in adults. Protective titers appeared 6 weeks after initial inoculation in 126 of 127 subjects and were maintained for at least 3 years in a 11 subjects. Mean maximum titer in subjects inoculated twice and three times after the initial vaccination were 393 mIU ml −1 at 6 weeks and 2745 mIU ml −1 at 7 months, respectively. Titers at 6 and 12 months after the initial vaccination were significantly higher in subjects with the 1.0 μg inoculation than with 0.5 μg. Titers in females were significantly higher than in males. The mean titer after inoculation was 1.1% of the convalescent titer in patients with acute hepatitis A. Neither adverse clinical events nor abnormal laboratory tests were observed after vaccination. Hepatitis A virus antibodies appeared reliably after inoculation with inactivated vaccine, persisting for at least 3 years. Although seroconversion rate was not age- or sex-dependent, the acquired titer was higher in children and females than in elderly males.