Rates of Haemophilus influenzae type B (Hib) infection in the UK have increased in recent years, despite the fact that England and Wales have been routinely vaccinating infants against the disease since 1992, researchers report in the British Medical Journal.

Hib infection is responsible for diseases such as meningitis, respiratory illness and blood poisoning.

The Hib vaccination campaign initially resulted in a reduction in reported cases among children, from 21.91 per 100,000 in 1992 to 0.65 by 1998, note Dr. Mary E. Ramsay and colleagues from the UK’s Health Protection Agency. This was followed by a decline in adult cases, probably because of reduced transmission from children to adults.

But from 1998, cases in children started to rise significantly, although remaining below pre-vaccination levels. In tandem with this, the rate of infection among adults also increased, and adult rates rose to exceed those seen before the vaccination programme.

This rise was associated with evidence of reduced immunity in older, unimmunised people, the authors note.

This lowered immunity “may have resulted from reduced transmission of the organism, providing fewer opportunities for natural boosting of immunity,” Ramsay and colleagues suggest.

The unanticipated effects of Hib vaccination show the value of proper surveillance, Ramsay’s group suggests. The high quality of surveillance in England and Wales allowed health authorities to react quickly, they note.

A national booster vaccination programme has been implemented for children younger than 4 years. “We anticipate that this campaign will rapidly induce herd immunity and prevent any further increase in infections in all groups,” the authors conclude.

Source: British Medical Journal, September 18, 2004.