Safety and immunogenicity of a new inactivated hepatitis A vaccine in concurrent administration with a typhoid fever vaccine or a typhoid fever + yellow fever vaccine.

Two clinical studies were conducted to evaluate the safety and immunogenicity of concomitant administration of a new inactivated hepatitis A (HA) vaccine and either a typhoid fever (Vi) vaccine or a combination of Vi and yellow fever (YF) vaccines. In study 1, 62 healthy adults received HA+Vi into the deltoid muscle on contralateral sides. In study 2, 59 healthy adults received HA and a combined Vi/YF vaccine into the contralateral deltoid muscles. Reactogenicity was evaluated for 14 days following vaccination. Blood samples (for antibody titration) were obtained prior to vaccination on days 0 and 28 in study 1 and prior to vaccination on day 0 and on days 14 and 28 in study 2. The overall rate of local reactions was 19% at the HA injection site and 75% at the Vi injection site in study 1; the rate of systemic reactions was 41%. In study 2, local reactions occurred at 27% and 78% of the HA and Vi/YF injection sites; the rate of systemic reactions was 42%. All reactions were transient. Twenty-eight days after vaccination, the seroconversion rate was 100% for HA antibodies and 90% for the Vi vaccine in study 1. Rates of seroconversion in study 2 were 100% for the HA vaccine, 92% for the Vi vaccine, and 100% for the YF vaccine. Although this study was not comparative, both tested combinations were safe and immunogenic, and their routine use for persons at risk, such as travelers, can be recommended.