[Significant decline of the number of invasive Haemophilus influenzae infections in the first 4 years after introduction of vaccination against H. influenzae type B in children].

OBJECTIVE: To evaluate the effect of four years of immunisation against Haemophilus influenzae type b (Hib) on the occurrence of invasive H. influenzae infection and of vaccine failure in children.
DESIGN: Descriptive.
METHOD: Through the Nederlands Signalerings-Centrum Kindergeneeskunde (NSCK; Dutch Paediatric Surveillance Unit), invasive H. influenzae infections in children under 15 years of age reported by paediatricians were registered from October 1993 until December 1997. On the basis of the NSCK data the incidence of invasive H. influenzae infections was determined for 1994-1997 in relation to the children's age.
RESULTS: The numbers of cases of invasive H. influenzae infection were 129 in 1994, 41 in 1995, 24 in 1996 and 8 in 1997. The decrease mainly concerned type b infections. The mean age at infection increased in the first two years after the introduction of vaccination. No apparent change in the clinical presentation of infection was observed. In four years of surveillance a total of nine cases of vaccine failure was reported.
CONCLUSION: The progressive effect of vaccination against Hib was reflected in the strong decline of the number of invasive Hib infections, mainly in the youngest children. In accordance with the high level of voluntary vaccination in the Netherlands (95.5% as of January 1st 1997) and the expected high vaccine efficacy the number of vaccine failures was low. A further beneficial effect for the youngest children may be expected from starting the vaccination scheme at a still earlier age.