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.
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.
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.
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.