The chief medical officer has recently recommended that all children in the United Kingdom aged 6 months to 4 years should receive a single dose of Haemophilus influenzae type b vaccine. This is in response to a rise in the incidence of Hib disease over the past four years. The reasons for the increase are complex, but evidence points strongly to an effect of a temporary change to the use of a Hib vaccine combined with diphtheria, tetanus, and acellular pertussis (DTaP).

Before the Hib conjugate vaccine was introduced in 1992, Hib was the most common cause of bacterial meningitis in children. Rapid control of Hib disease was achieved by combining routine infant immunisation at 2, 3, and 4 months of age with a catch-up programme for children aged up to 4 years. Initially Hib vaccine was given as a separate injection, but in 1996 a combined DTP-Hib vaccine was introduced. Uptake of the vaccine was high, and the number of confirmed cases of type b infection fell from 855 in 1992 to 37 in 1998, but since 1999 a steady increase …