HEALTH: SECOND OPINION

HOW much harm does immunisation do to healthy children? This question has been asked for 200 years, since the earliest days of vaccination against smallpox. Now, it has resurfaced with a report suggesting that the current measles vaccine may increase the risk of children developing an unpleasant and dangerous bowel disorder, Crohn's disease.

Crohn's disease is a chronic inflammation of the intestine, usually affecting the small bowel but sometimes the large bowel as well. It causes attacks of pain and diarrhoea, and poor appetite leads to loss of weight. Its cause is unknown, but it is becoming more common. Between 3,000 and 4,000 new cases now occur each year in England and Wales.

A possible link between some cases of Crohn's disease and infection with natural, wild measles was first reported in 1993, when the measles virus was found in the intestinal cells damaged by the disease. More recent research (Lancet, vol 345, pp1,071-3) has suggested that children immunised against measles using a living vaccine may be at increased risk of later developing Crohn's disease, possibly because the vaccine is given at a younger age than that at which children used to catch wild measles. Follow- up of a group of children given the vaccine in 1964, and another group of unvaccinated children, found that the disease was three times as common in the adults vaccinated as children.

This study has been criticised on the grounds that the two groups of children were too different for a valid comparison, and the Department of Health has reassured parents about the vaccine programme. But immunisation with several living virus vaccines does carry small risks. The original vaccine against smallpox caused a serious brain disease in one in every 10,000 children; living polio vaccine still carries a risk of one in 1,000,000 of causing paralytic polio, and the mumps component of the original measles/mumps/ rubella (MMR) vaccine had to be withdrawn because it was causing a form of meningitis. In each case the risks from the vaccine had to be balanced against the risks of the disease.

Parents today have no personal experience of epidemic childhood infections - and little idea of the chances of the old diseases re-emerging. Yet with the exception of smallpox, now officially extinct, none of the old scourges of child health has been finally defeated throughout the world. Dramatic evidence of this is emerging from the former Soviet Union. Since 1990 an epidemic of diphtheria has been sweeping through the new independent states, and the World Health Organisation reports that 14 of the 15 states were affected in 1994 with a total of 47,802 cases and 1,746 deaths.

Parents of children who develop a serious illness after immunisation find it hard to accept that, overall, immunisation is of benefit. The child who is damaged by a vaccine might not have been damaged by the disease. Research is continuing into safer vaccines using bio-engineering techniques, but manufacturers in the US are reluctant to invest in them because of the vast punitive damages awarded if they go wrong. No way has yet been found to balance the price paid by the individual damaged child for the benefits gained by the child community as a whole.