Effect of nationwide vaccination of 3-month-old infants in the Netherlands with conjugate Haemophilus influenzae type B vaccine high efficacy and lack of herd immunity

OBJECTIVE: The effect of nationwide vaccination in The Netherlands with conjugate Haemophilus influenzae type b vaccine on the incidence of H. influenzae meningitis was assessed in the first 3 years after the introduction of vaccination to the birth cohort at 3 months of age. STUDY DESIGN: Children in The Netherlands born after April 1, 1993, were vaccinated at the age of 3, 4, 5, and 11 months. Children older than 3 months at the inception of the H. influenzae type b vaccination program were not immunized. The number of cases among the vaccine cohort was compared with the number in a historical control group of children born in the period April 1, 1990, and April 1, 1993. RESULTS: The total number of patients with meningitis caused by H. influenzae type b reached a low, but constant level, that was expected for absence of herd immunity. Among children in the vaccine era group 22 cases occurred, whereas among the historical control group (prevaccine era) 342 cases were found. In the vaccine era cohort, 2 patients with H. influenzae type b meningitis had been vaccinated three times, 13 received one or no vaccine dose because of their age, and 7 were not vaccinated for religious or logistic reasons. The number of cases among nonvaccinated children older than 3 years and the number of H. influenzae meningitis cases caused by strains other than type b did not change. CONCLUSIONS: Conjugate H. influenzae type b vaccine prevents H. influenzae type b meningitis very effectively (99.4%) in children vaccinated twice or more. To reach rapid prevention of all H. influenzae type b disease simultaneous introduction of H. influenzae type b vaccination of children at various ages is recommended