Immunoglobulin deficiency in children with Hib vaccine failure.

Immunoglobulin deficiency has been reported in 21% of UK children with Hib vaccine failure but its clinical significance and long-term consequences are not known. This study aimed to estimate the prevalence of immunoglobulin deficiency in children with Hib vaccine failure several years after infection and to determine their risk of recurrent infections. The families of children who developed invasive Hib disease after prior immunisation were identified through national surveillance. A completed questionnaire and blood sample was provided by 170 children at a median of 4 years after infection, equivalent to 1035 child-years of follow-up. Nineteen (11.2%) children had immunoglobulin deficiency, including IgA (n=12), IgM (n=5) and all three immunoglobulin classes (n=2). Immunoglobulin deficiency was associated with younger age (<2 years) at initial Hib disease (12/19 [63.2%] vs. 60/151 [39.7%], P=0.05) and parental reporting of their child receiving >2 antibiotic courses annually in early childhood (11/19 [57.9%] vs. 39/151 [25.8%], P=0.004].). In a logistic regression model, Hib vaccine failure cases that had received multiple antibiotic courses in early childhood were 3.8 times (95% CI, 1.4-10.6; P=0.01) more likely to be immunoglobulin deficient at follow-up than those with fewer or no antibiotic courses. Thus, the prevalence of immunoglobulin deficiency in children with Hib vaccine failure at a median of four years after infection is half that reported at the time of the original infection. A proportion of children with Hib vaccine failure, especially where it occurs at a young age, appear to have a maturational delay in development of normal immunoglobulin concentrations.