DOES IMMUNOGLOBULIN INTERFERE WITH THE IMMUNOGENICITY TO PASTEUR MERIEUX INACTIVATED HEPATITIS-A VACCINE

Background/Aims: The aim of this study was to compare the immunogenici ty of Pasteur Merieux (P.M. s.v.) inactivated hepatitis A vaccine when given alone with its immunogenicity when given in combination with im munoglobulin. Methods: We enrolled 80 healthy volunteers who were sero negative for anti-HAV. Forty subjects (group A) were given two doses o f vaccine at 0 and 6 months plus 4 ml of immunoglobulin given simultan eously with the first vaccine injection; and 40 subjects (group B) wer e given vaccine alone. The population characteristics (age, sex, heigh t and weight) of the two groups were comparable. Results: Anti-HAV ant ibody was detectable at week 1 in 100% of group A and in 5.7% of group B, and in 100% of both groups at 4 and 8 weeks. Seroconversion rates (greater than or equal to 20 mIU/ml) were 97.4% in group A and 100% in group B at week 24 and were 100% in both groups 4 weeks after a boost er injection at 6 months. The antibody response level was lower after concomitant administration of vaccine with immunoglobulin. The antibod y geometric mean titer was higher at week 1 in subjects who had been g iven vaccine and immunoglobulin, but nearly 50% lower at week 4 and th ereafter, indicating inhibition of the vaccine-induced immune response by immunoglobulin. At week 28, i.e. 4 weeks after the booster injecti on, geometric mean titers had increased about 13-15 times in both grou ps, reaching highly protective antibody levels (3351 mIU/ml in group A and 5843 mIU/ml in group B). No serious adverse effects were observed during the follow-up. Conclusions: These data indicate that P.M. s.v. hepatitis A vaccine is highly immunogenic and safe, even when given s imultaneously with immunoglobulin. Despite the interference of the imm unoglobulin with the active immune response, individuals who were immu nized passively plus actively also developed high titers of anti-HAV a ntibody. It is therefore reasonable to expect that this inhibition wil l not affect the overall protection conferred by the vaccine.