Low serum serotype-specific pneumococcal antibody concentrations in young children with Haemophilus influenzae serotype b (Hib) vaccine failure

Serotype-specific pneumococcal antibody concentrations were measured in 164 children with Hib vaccine failure prior to routine pneumococcal immunisation. Compared with age-matched controls, a higher proportion of cases had non-protective antibody concentrations (<0.35 μg/ml) for 7/9 (78%) serotypes tested among 2–4 year-olds, 4/9 (44%) among 5–7 year-olds, 1/9 (11%) among 8–11 year-olds and 0/9 (0%) among 12–15 year-olds (χ2 for trend = 14.0, p = 0.0002). Cases aged 2–4 years were also more likely to have non-protective antibody concentrations against more serotypes than controls, suggesting that children with Hib vaccine failure may have an intact but physiologically delayed ability to develop protective antibody concentrations against encapsulated organisms.