Background: The introduction of vaccines against Haemophilus influenzae type b (Hib) has had a substantial impact on Hib infections. Their use has established their excellent safety profiles but occasional adverse effects have been reported.
Case report: A 4 month-old infant was admitted for a severe form of Hib meningitis with septicemia whose first manifestations developed 3 hours after the first immunization with a conjugate vaccine against Hib (PRP-T). The outcome was good without any sequelae.
Discussion: A dramatic decrease in serum antibodies due to antigen-antibody reaction during the first days after immunization has been reported; this mechanism and some epidemiological data could favor the hypothesis that the vaccine is responsible for the infection, at least the unconjugated vaccines.
Conclusion: Any fever occurring in the immediate post-immunization period must alert the possibility of a Hib infection.