Time course of hepatitis A virus antibody titer after active and passive immunization

To investigate the antibody titer necessary to prevent hepatitis A virus infection, either 15 or 7.5 mg/kg of immune serum globulin was injected into 10 antihepatitis A virus negative volunteers and their serum antihepatitis A virus titers were observed for 28 wk. In addition, antibody titers were observed for 96 wk in a phase 1 clinical trial of a hepatitis A vaccine. The two studies were then compared to assess the immunogenicity of the vaccine and the persistence of the antibody. Serum‐neutralizing antibody titers that were greater than or equal to 4 (considered as positive) persisted for 18 wk and 14 wk after the injection of 15 and 7.5 mg/kg of globulin, respectively. Hepatitis A virus vaccine recipients showed adequate neutralizing antibody titers, with the groups receiving 1, 0.5 and 0.25 μg/dose showing titers of 4 5.5 , 4 4.7 and 4 4 , respectively, at 18 mo after the third inoculation. These findings suggested that effective blood antibody titers were likely to be retained in the 1.0 μg or 0.5 μg/dose groups for at least several years. Moreover, the serum antihepatitis A virus titers demonstrated by a modified radioimmunoassay changed in parallel with the neutralizing antibody titers in the volunteers injected with globulin. (H EPATOLOGY 1992;15:983‐988).