[Effectiveness of Haemophilus influenzae B-diphtheria conjugate vaccination in German children].

Background: In 1990 the Haemophilus influenzae b-Diphtheria conjugate vaccine (Hib-D) was introduced in Germany. In addition, most children under 18 months of age failed to develop protective levels of Hib antibodies in response to systemic infections.
Methods: To evaluate the protective efficacy of the Hib-D vaccine in Germany a post marketing case-control study was performed during 1.5. 1990-30.4. 1992. Surveillance for invasive Hib-infections was maintained by pediatricians of 8 hospitals in the Rhein-Main area. The antibody responses to Hib were evaluated by ELISA at the onset (days 0-3) and during remission of disease.
Results: During the first year of the study 23 cases per 100,000 children of invasive Hib-infections were recorded. Of these children, 15 suffered from meningitis, 6 from epiglottitis and one from cellulitis and pericarditis respectively. None of these patients had been vaccinated except for one, who received two injections of Hib-D. Due to increased acceptance of the Hib-D vaccine we found a significant reduction of invasive Hib-infections (6 cases per 100,000 children) in the second year of the study. Again, of these children only one child was vaccinated. As expected, in all patients investigated the initial Hib antibody level was below 1 microgram/ml. The development of Hib specific immunity to invasive disease was clearly age dependent: 10 of 11 children below 18 months failed to produce any Hib antibodies (> 0.15 microgram/ml) in response to their infection. In contrast 8 of 10 children older than 18 months developed protective antibody levels to Hib.
Conclusions: The incidence of serious Hib-disease has significantly decreased in Germany since the introduction of the Hib-D vaccine. Because no other Hib vaccine was licensed in Germany our data confirm efficacy and safety of Hib-D reported previously. In addition, children, who contracted disease before 18 months of age, remain susceptible to Hib and require active immunization for protection.