Four and one-half-year follow-up of the effectiveness of diphtheria-tetanus toxoids-acellular pertussis/Haemophilus influenzae type b and diphtheria-tetanus toxoids-acellular pertussis-inactivated poliovirus/H. influenzae type b combination vaccines in Germany

BACKGROUND: Recently an increase in the number of invasive Haemophilus influenzae type b (Hib) cases was observed in the United Kingdom, which coincided with a temporary change from diphtheria-tetanus toxoids-wild-type pertussis to diphtheria-tetanus toxoids-acellular pertussis (DTaP) Hib vaccines. A study in Germany based on approximately 2 years of follow-up, estimated vaccine effectiveness (VE) of DTaP/Hib and DTaP-inactivated poliovirus/Hib combination vaccines against invasive Hib disease to be high. OBJECTIVES: To assess VE of DTaP-containing Hib vaccines against Hib in Germany with the use of extended follow-up of case surveillance and vaccine uptake. SUBJECTS AND METHODS: Cases with confirmed systemic Hib infections in children born between June 1, 1996 and December 31, 1998 were ascertained by a nationwide active surveillance system from January 1998 through June 2002. A representative subcohort of 667 children born in the same time frame was randomly sampled in a nationwide vaccine coverage survey. VE was determined with a case-cohort approach of Cox regression with time-dependent covariates. RESULTS: Thirty-six cases of Hib disease were reported. Of these, 10 were vaccinated with DTaP-containing Hib vaccines only and 20 were not vaccinated. Of the 10 vaccinated cases, 4 had received an incomplete primary series (1-2 doses), and 6 had received the full primary series (3 doses), 3 of whom also received the booster dose. VE of combination vaccines against invasive Hib infection was 89.6% [95% confidence interval (CI), 67.0-96.7] for an incomplete primary series, 96.7% (95% CI 87.7-99.1) for a full primary series and 98.5% (95% CI 94.5-99.6) for a booster dose (irrespective of priming). CONCLUSION: Hib combination vaccines containing acellular pertussis antigens continue to be highly effective in Germany.