Tolerance and immunogenicity of the simultaneous administration of virosome hepatitis A and yellow fever vaccines

Background: The purpose of this study was to evaluate the tolerance and imm unogenicity of a hepatitis A vaccine using immunopotentiating reconstituted influenza virosomes (IRIV) as adjuvant when administered simultaneously wi th a yellow fever vaccine (YFV). Method: An open prospective trial with two parallel groups was conducted wi th 105 volunteers to study the effect of these vaccinations on the anti-hep atitis A virus (HAV) antibody response. Half of the volunteers (53) receive d one dose of IRIV-HAV vaccine (Epaxal(TM)) and one dose of live attenuated YFV (Stamaril(TM)) on the same day at two different sites. Fifty-six volun teers were given a single injection of IRIV-HAV as a control group. Anti-HA V titers were measured at days 14, 28, months 3, 12, 13, and 24 using a sta ndardized test (Enzymun test Anti-HAV). Neutralizing yellow fever antibodie s were measured at days 14 and 28 for the YFV recipients. Regarding vaccine tolerance; the volunteers were asked to record all their adverse reactions on a standard report sheet for the 6 days following the immunization. Results. Seroconversion rates for HAV were 88% after 14 days and 100% after 4 weeks. There was no statistically significant difference between the two groups every time the titers were checked (IRIV-HAV vs HAV only: D14: 81 v s 101; D28: 275 vs 368; M3: 153 vs 169; M12: 117 vs 226; geometrical mean t iters (GMT) in mIU/mL). However, lower titers were found among male volunte ers, and were not attributable to YFV administration. The seroconversion ra tes for YFV were 90% after 14 days and 96% after 4 weeks. No serious genera l side-effects and only mild local reactions were reported. The administrat ion of a booster of IRIV-HAV at 12 months resulted in a 24-fold increase in GMT. Conclusion: When needed, the simultaneous administration of the IRIV-HAV an d YFV is immunogenic, safe and well-tolerated, as volunteers seroconverted to both antigens, with no cross-interference.