Immunogenicity and safety of hepatitis A vaccine at different vaccination intervals among adults aged 18 years and above: Interim results

This study aims to evaluate the immunogenicity and safety of hepatitis A vaccine administered with one or two doses among adults. Participants aged 18 y and above were recruited, with blood samples collected prior to vaccination for anti-HAV antibodies screening. All participants received a single dose of hepatitis A vaccine. Participants who tested negative for anti-HAV antibodies before vaccination were randomly assigned to four groups to receive the second dose at different intervals. Blood samples were collected for antibody testing. Adverse events were reported within 28 d after each vaccination for safety assessment. A total of 1,042 participants were included in study analysis. The seroprevalence of anti-HAV antibodies was 52.56%, with the lowest seroprevalence observed among adults aged 36–40 y. The overall seroconversion rate 1 month after the first dose of hep A vaccine was 67.68%. For participants in group A, the second dose was administered at a 6-month interval, both the seropositivity and seroconversion rates reached 100%, with a GMC of 3602.44 IU/L 1 months after the second vaccination. Difference of GMCs had no statistical significance across age groups. The incidence of adverse reactions (ARs) within 28 d after second vaccination in group A was 3.85%. No serious adverse events (SAEs) related to vaccination were reported. This interim analysis highlights the susceptibility of adults to hepatitis A virus (HAV). One or two doses of hepatitis A vaccine demonstrated good immunogenicity and safety in adults.