Childhood illnesses may be on the wane, but are vaccines damaging our children's immune systems?
Taking a small child for his or her "jab" is not something any parent greatly looks forward to, even if most appreciate that immunisation has virtually wiped out some childhood diseases.

But reports that the combined measles, mumps and rubella (MMR) vaccine is being linked to a rise in incidence of two serious illnesses has caused more parental unease than usual. The issue is being taken seriously by the Government, with the Health Minister, Tessa Jowell, together with the Chief Medical Officer, Sir Kenneth Calman, set to meet concerned parents and scientists next month.

The combined MMR vaccine was introduced in 1988 and is given to babies between 12 and 15 months old, with a pre-school booster also offered for three-to-five-year-olds. All three viruses are live, modified to produce an immune response sufficient to protect children against the diseases themselves.

Measles, mumps and rubella are now rare in Britain, as are their sometimes serious complications: measles was once a cause of blindness and brain damage, and before the vaccine was introduced, 90 children in the UK died from it annually.

While the MMR can trigger mild fever and rash, serious side-effects are thought to be rare. The risk of developing encephalitis after vaccination has been put at 1 in 1 million, compared to the 1 in 5,000 risk after measles; one-third of these cases would be left with permanent brain damage. One in 1,000 children may have a convulsion after immunisation, compared with 10 times this number after measles.

Parents of brain-damaged children, who have formed JABS (Justice, Awareness, Basic Support) say the risks of vaccination are higher than the Government admits. Government experts however, say there is no scientific evidence to back their claims.

But new research by doctors at the Royal Free Hospital, London, suggests a link between MMR and two serious illnesses: Crohn's disease, a chronic gastrointestinal tract disorder, and autism. One of the doctors, Andrew Wakefield, published research linking the MMR to Crohn's in The Lancet two years ago. He found that vaccinated children were three times more likely to develop Crohn's, but the Government dismissed his findings as inconclusive. In an interview with the GPs' magazine Pulse, he says he now has enough evidence for the Government to conduct an independent review of vaccination policy.

The five as yet unpublished papers are believed to include an epidemiological study involving some 10,000 children, which found a dramatic increase in Crohn's disease since the introduction of measles vaccination. The Royal Free doctors also say they have found the measles virus in Crohn's disease tissue. Cases of autism, it is suggested, may result from an extremely rare reaction to bowel disease.

It may be the combination of three live viruses given simultaneously which could be responsible for a serious assault on the immune system, the doctors believe. Sir Kenneth has said in response that "rigorous scrutiny" by scientists has established there is no link between MMR and Crohn's or autism but that he will consider any new evidence. In the meantime,what should parents do?

They can, of course, choose not to have their child immunised. But if enough parents took this road, then the diseases and their complications would return.

One option is to ask for the three separate vaccines to be administered at intervals, to reduce the risk of damaging the immune system. Some parents are already doing this; many GPs are happy to comply.

Nothing is risk-free. Current evidence shows the risk of damage from these diseases to be far higher than the vaccines which prevent them.