Over recent decades, the global incidence of hepatitis A virus infection has been reduced by improvements in sanitation infrastructure and through immunization programs. The immunogenicity and field efficacy of the inactivated hepatitis A vaccine (Havrix™, GSK, Belgium) has been demonstrated in clinical trials, population-impact studies as well as in several outbreak settings. However, immunological data in older populations are limited, with only few studies assessing the immune response of this vaccine in adults aged ≥ 40 years. This retrospective pooled analysis of 4 2-dose primary vaccination studies compared the immunogenicity and safety of the inactivated hepatitis A vaccine in adults aged ≥ 40 years with subjects aged 20-30 years (control group; N = 80 in each group). Fifteen days after the first vaccine dose, 79.7% (95% CI: 68.8-88.2) and 92.3% (95% CI: 84.0-97.1) of subjects were seropositive in the ≥ 40 years and control groups, respectively; 97.5% (95% CI: 91.2-99.7) and 97.4% (95% CI: 91.0-99.7), respectively, were seropositive one month after the first dose. All subjects in both groups (95% CIs: 95.4-100 and 95.3-100, respectively) were seropositive one month after the second dose. Safety profiles were similar in both groups. In conclusion, the inactivated hepatitis A vaccine induced similar immune responses in adults aged ≥ 40 and 20-30 years one month after the first and second dose whereas younger subjects may demonstrate a higher seroconversion rate 15 days after the first dose.
Keywords: CI, confidence interval; ELISA, enzyme-linked immunosorbent assay; GMC, geometric mean concentration; HAV outbreak; HAV, hepatitis A virus; HNIG, human normal immunoglobulin; Havrix™; TVC, total vaccinated cohort; UK, United Kingdom; WHO, World Health Organization; immunogenicity; inactivated hepatitis A vaccine; older adults; rapid response.