As recently as the late 1980s, measles killed 17 British children in what was described as a relatively minor outbreak.

This only hints at the destructive power of a virus, which has largely been forgotten by the UK public.

In 1988, the year after Britain's last measles outbreak, the MMR vaccination was introduced.

Weakened viruses

The MMR vaccine has greatly reduced rates of the disease

It is formed from weakened, but still living versions of all three viruses. This allows the body to generate immune resistance to them without developing a full-blown infection.

Measles can kill, but is more likely to lead to serious complications, particularly in the very young. These can include pneumonia or bronchitis, convulsions, and even meningitis.

Mumps, characterised by painful and swollen glands in the head and neck, can cause permanent damage to the testicles, nervous system and hearing.

And Rubella, or German Measles, if developed late in pregnancy, can lead to serious birth defects such as deafness, blindness, cardiac problems and brain damage.

When the first measles vaccine was introduced in the 1970s, incidence of the disease more than halved. The MMR virtually eliminated the disease in the UK.

The World Health Organisation estimated that without MMR immunisation, worldwide around three million children would die each year.

First scare emerges

Crohn's Disease, an inflammatory and incurable condition which affects the lower bowel was first linked to the measles virus by a team led by Dr Andrew Wakefield at the Royal Free Hospital in North London in 1994.

They speculated that damage to the blood vessels surrounding the gut, typical of Crohn's, might have been caused by the virus.

In addition, they suggested that exposure to measles just after birth might make someone more likely to get Crohn's later.

GPs have seen immunisation rates plummet

A Swedish study, published shortly afterwards, identified three of four children, born of mothers who contracted measles when pregnant, who went on to develop Crohn's.

However, if measles was the culprit, this had to be proved either statistically or by finding traces of the virus in the gut of Crohn's sufferers.

Subsequent research projects could do neither, and the results of the Swedish study could not be reproduced by other studies.

New Crohn's evidence

This month, another study from the Royal Free claimed that children who contracted measles and mumps close together were six times more likely to contract Crohn's in later life.

In 1998, the editor of the British Medical Journal declared the theory "dead" after reviewing all the available evidence.