To jab or not to jab?

It is the name given to a single vaccine, administered to 15-month-old babies against measles, mumps and rubella (German measles).

Why is it controversial?

A 1998 study by researcher Andrew Wakefield linked MMR to autism, a severe brain condition affecting children. The combination of three live viruses used in the triple vaccine may be seriously compromising their immune systems, he argued.

What about other studies?

Most scientific evidence suggests no link. The Medical Research Council (MRC) last month said autism was probably caused by genes that interact to create special susceptibility. Autism cases seem to be rising because we are more aware of the condition, the report argued. Last month Dr Wakefield was forced to resign from his post at the Royal Free Hospital, London.

What dangers are posed by measles, mumps and rubella?

In one in 100,000 cases, measles can cause brain illness and death. Mumps can lead to sterility in adult males while rubella in early pregnancy can cause birth defects in babies.

What are the dangers of the current MMR boycott?

Around 95 per cent of children have to be vaccinated to prevent measles, but autism fears have reduced uptake to less than 80 per cent in most British cities. As a result, doctors now fear the country faces a serious risk of a measles outbreak.

What about other countries?

Most nations still use MMR. However, following controversy in Britain, MMR take-up in Ireland has also plummeted. This boycott led to a measles outbreak in Dublin last year that killed two children, and left many more permanently damaged.

So why not administer three separate vaccines?

Single vaccines would cause major bureaucratic headaches, say health officials. Delays and failures to take booster jabs would leave thousands unprotected. Before MMR, they say, there were 16 deaths a year from measles; mumps was the leading cause of viral meningitis; and rubella caused devastating disabilities to the unborn. Now we are free from these diseases - so long as babies are vaccinated.