Concentration and avidity of anti-Haemophilus influenzae type b (Hib) antibodies in serum samples obtained from patients for whom Hib vaccination failed.

Haemophilus influenzae type b (Hib) conjugate vaccines are extremely effective in protecting infants and children from invasive Hib infections; however, vaccine failures do occur. The anti-Hib antibody production was studied both quantitatively and qualitatively in 12 patients who experienced Hib failure, all of whom had normal serum immunoglobulin concentrations and all of whom were without clinical risk factors for invasive Hib disease. Both anti-Hib antibody concentration and immunoglobulin-G2 anti-Hib antibody avidity were significantly lower in patients who experienced Hib failure, at onset of disease and after reconvalescence, when compared with controls. This finding suggests that the patients who developed invasive Hib disease--despite having received 3-4 Hib conjugate vaccinations--were inadequately primed by these vaccinations.