The Hib immunization programme in the Oxford region: an analysis of the impact of vaccine administration on the incidence of disease

In May 1991 an immunization programme against Haemophilus influenzae type b (Hib) infection began within the Oxford region. We validate a deterministi c mathematical model of Hib by comparison with the incidence of disease in the Oxford region, 1985-97. The comparison of model results with observed o utcome allows an exploration of some of the poorly understood properties of the immunization programme. Model results and observed incidence are consi stent with a vaccine that blocks the acquisition of carriage. Similarly, th e data suggest that factors other than experience of Hib carriage are likel y to have generated acquired immunity to Hib disease prior to the introduct ion of vaccination. Hence it is unlikely that waning of vaccine-derived pro tection will result in a resurgence of disease. The inclusion in the immuni zation schedule of a booster dose, as used in other countries, would have p rovided very little extra benefit.