IMMUNOGENICITY AND REACTOGENICITY OF A HAEMOPHILUS-INFLUENZAE TYPE-B TETANUS CONJUGATE VACCINE WHEN ADMINISTERED SEPARATELY OR MIXED WITH CONCOMITANT DIPHTHERIA-TETANUS-TOXOID AND ACELLULAR PERTUSSIS-VACCINE FOR PRIMARY AND FOR BOOSTER IMMUNIZATIONS

With an increasing number of new vaccines available for routine childh ood immunization, combination vaccines are needed in order to maintain or achieve a high compliance with recommended immunization programmes . In a prospective, randomized, comparative, multi-centre study, 822 h ealthy infants were enrolled to receive three doses of either a candid ate or a commercially available Haemophilus influenzae type b (Hib) va ccine concomitantly with diphtheria-, tetanus-acellular pertussis (DTa P) vaccine. Study subjects were randomly allocated to one of the follo wing groups: (1) separate, or (2) mixed injection of DTaP and candidat e Hib vaccine, or (3) separate injection of DTaP and commercial Hib va ccine. One year later the first 189 study subjects received either sep arate or mixed injections of the same Hib and DTaP vaccines as booster doses. Evaluation of reactogenicity was based on diary cards complete d by parents. Immunogenicity was documented by measuring IgG antibody concentrations in serum samples taken before and 4 weeks after primary and booster vaccination. No serious adverse events occurred and most local and systemic reactions were mild to moderate. Booster doses were more reactogenic than primary doses with all groups. Antibody concent rations against pertussis antigens were similar to those seen with DTa P alone, All but one subject had protective antibody concentrations ag ainst diphtheria and tetanus, Primary immune response to the Hib vacci ne was significantly lower in the group receiving the mixed Hib-DTaP v accine, however, greater than or equal to 95% of vaccinees had anti-Hi b antibody concentrations greater than or equal to 0.15 mu g/ml and th ere was a marked booster response (> 100-fold) in all groups. Conclusi ons Mixing DTaP and Hib vaccines for primary immunization caused a dec rease in anti-Hib antibody response, although after primary immunizati on as after booster doses, all subjects showed antibody concentrations considered to be protective for invasive Hib disease. Mixing of the v accines did not result in increased reactogenicity.