The whole-cell DPT (diptheria-tetanus-pertussis) vaccine is not very effective, protecting less than half the children vaccinated.

New research from Sweden and Italy has shown that the vaccine is effective in just 48 per cent and 36 per cent of cases respectively.

American experts have tried to explain away the findings by explaining that the children who were studied received just three doses of the vaccine, whereas five doses are given in countries such as the US. In addition, the study coincided with a pertussis epidemic, and so the childen were more exposed to the disease. (Perhaps the vaccine only works when the disease isn't around!)

However, children given the new acellular version of the vaccine fared better, with three of the four vaccines showing efficacy rates of between 84 per cent and 85 per cent. The one failure was the fourth vaccine, which gave protection in just 58 per cent of cases.

The study, which began in 1992, involved more than 25,000 children.

News of the relative success of the acellular vaccine has come not a moment too soon for American health authorities, who have revealed that pertussis rates have increased cyclically since the early 1980s, with peaks occurring in 1983, 1986, 1990 and 1993. This is despite an effective nationwide immunization programme. Since the last peak, the number of cases has fallen during 1994 and the first two quarters of 1995 (JAMA, August 9, 1995).