Concentration and Avidity of Anti–Haemophilus influenzae Type b (Hib) Antibodies in Serum Samples Obtained from Patients for Whom

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. Haemophilus influenzae type b (Hib) conjugate vaccines have proven to be extremely effective in protecting in-fants and children from invasive Hib infections [1, 2]. However, a small number of children still develop in-vasive Hib disease despite vaccination. In The Nether-lands, vaccination with Hib conjugate vaccine was in-corporated into the National Vaccination Program fo