This entry was recommended on 12th February 2003 and accepted on the 18th February. The edited version of the entry is here.

The MMR vaccine protects against measles, mumps and rubella - three disease-causing viruses. It is normally given in two injections, the first at 12-15 months and a booster at 4-6 years. It contains live, attenuated¹ forms of the viruses that produce the three diseases that, when injected, allow the child's immune system to respond to the virus as it would the normal virus, developing the necessary antibodies to protect against the viruses without risk of death or infecting others.

After the first injection, 95% of children are immune; after the second injection, 99%.

The diseases the MMR vaccine immunises against

Measles

Worldwide, this accounts for one million deaths annually - 10% of all deaths of children aged five years and under. In a healthy child, however, it is usually uncomplicated, involving only about two weeks off school. 1 in 100 children need hospital admission. It is, however, far more serious for a child with malnutrition or a co-existing disease.

Possible effects

• Fever
• A distinctive rash
• Red, painful eyes
• Swollen glands
• Loss of appetite
• Death²

Possible complications are if a child is infected early in life and the virus later resurfaces at puberty - there is then a 1.5% chance of death or serious persisting complications.

Mumps

This is most common in school-aged children, but can occur at any time.

Possible effects

• Central nervous system complications, including meningitis³. This can result in long term complications such as permanent brain damage or death.
• Fever
• Malaise
• Headache
• Inflamed parotid gland
• Inflamed, painful testicles⁴
• Sterility, if untreated in adult males
• Pancreatitis⁵
• Deafness, usually with some recovery⁶
• Spontaneous abortion, if during pregnancy

Rubella

Rubella, commonly known as German measles is usually a trivial illness for young or primary-school-aged children.

Possible effects

• Malaise
• Rash and fever for 2-3 days
• Headache
• Conjunctivitis
• Sore throat
• Coughing
• Swollen glands
• Joint pains⁷
• Encephalitis⁸
• Bleeding disorders⁹
• Spontaneous abortion, if during pregnancy

Complications arise if a mother contracts rubella during the first half of pregnancy. The result in this case can be congenital rubella syndrome.

Babies born to mothers who develop rubella during pregnancy are likely to be born with one one or more of these problems:

• Deafness
• Blindness
• Heart problems
• Brain damage resulting in permanent learning difficulties

The results of the MMR vaccine¹⁰

Before immunisation was widely available in the UK, approximately 500,000 children contracted measles annually, and 100 of these died from it. In 1988, this had fallen to 13 deaths annually and since 1992 there have been no acute measles deaths reported in the UK.

During 10 years of vaccination, there has been a decrease by a factor of ten in the incidence of mumps. Mumps is, therefore, no longer a leading cause of viral meningitis.

Since 1988, there has been also been a decrease by a factor of ten in the notifications of rubella. Due to vaccination, fewer people transmit rubella to pregnant women, which, as described above, can permanently harm the child. In 1970 to 1979, there were 454 congenital rubella births in the UK; in 1990 to 1999, there were only 46 of these births.

Herd immunity

If a sufficiently high proportion of all people are vaccinated against a disease, herd immunity is achieved. This results in a dramatically-reduced risk of infection for any unvaccinated individuals or vaccinated individuals where the vaccine hasn't resulted in full immunity¹¹. 95% of people must be vaccinated with the MMR vaccine for herd immunity to measles.

Herd immunity also protects those at the greatest risk to the illnesses but who cannot receive the vaccinations. For example, children with transplanted organs are given immunosupressent drugs and those born with immunodeficiency disorders. These two groups of children cannot be vaccinated and, if they catch one of the diseases, will almost certainly die. If achieved, herd immunity greatly reduces their chance of catching the diseases.

Anti-vaccine campaigners

For a number of reasons, there are people who do not think that the MMR vaccine, or sometimes vaccines in general, are safe. This may be due to bad publicity about vaccinations; a philosophical objection to vaccinations or, very occasionally, concern about the payments GPs¹² receive for meeting immunisation targets. Alternatively, there may be a belief that the diseases are not very significant or that immunisation obtained naturally is preferable to the vaccinations.

The alternative view is that vaccinations are safer than having the disease itself and that herd immunity allows any unvaccinated people a degree of protection against the disease.

The link of the MMR vaccine to autism

Asperger's syndrome is a mild form of autism. Autism affects nearly 1 in 1000 children and results in the child being withdrawn - interested in objects instead of people - and often unable to communicate normally vocally.¹³

In 1998, a paper by Dr Wakefield was published in The Lancet that described a link between MMR and developmental regression and bowel disturbances. The term autistic enterocolitis was used to describe the syndrome thought to be caused by the MMR vaccination - apparent autistic regression, abdominal pain and diarrhoea.

Autistic children often develop the signs of autism shortly after receiving the MMR vaccine. Between 1988, when the MMR vaccine was widely introduced in the UK, and 2002, there was a significant rise in the number of children diagnosed with autism.

Public response to the link

From 1998 to the time of writing, 2003, this link of the MMR vaccine to autism was frequently reported in the UK media. Despite the advice from the UK government that the MMR vaccine was safe, a significant proportion of parents declined to have their children immunised. In 1999, approximately 90% of children received the first immunisation; in 2002, approximately 80% of children received it - the proportion of unimmunised children roughly doubled.

The view of the scientific community

Among scientists¹⁴, there is a widespread belief that this link is not present for five main reasons:

1. The rise in autism levels started before the MMR vaccine was widely introduced. It is attributed to better diagnosis of autism as the condition became more widely known. If a newly-introduced environmental factor causes a condition, there must be a sharp increase in the incidence of the condition, a short period of time after the environmental factor was first introduced.



2. The largest study carried out to investigate the possible link between the MMR vaccine and autism was carried out in Denmark from 1991 to 1998. 537,303 children were involved - of them only 440,655 were immunised. No increased risk of autism was found for those who were immunised compared to those who were not.¹⁵



3. It is frequently stated that a child developed autism soon after the MMR vaccine. However, autism is first recognised by parents at an age just after when the MMR vaccine is first given. The MMR vaccine is given at about 13 months, autism is usually first recognised at the age of about 24 months. While the MMR vaccine could be given at a later age, the risk to the child of permanent damage or death due to measles is approximately doubled between the ages of 13 months and 24 months.



4. The original study that suggested the link to autism was of only 12 children. Scientifically-sound studies consist of thousands of subjects and are repeatable by independant scientists but neither was the case here.



5. The study was retrospective¹⁶ and lacked a control group¹⁷.

However improbable a link seems, it is not certain that it doesn't exist. Based on all the available evidence¹⁸, the risks, if they do exist, are far outweighed by the benefits of the vaccine.

The possibility of separate vaccinations

In spite of the scientific evidence against the link, there are parents who do not wish to have their children vaccinated with the MMR vaccine. Therefore, instead of leaving their children unimmunised, three separate vaccinations have been suggested.

There are three main reasons that it is regarded as preferable to have the MMR vaccine instead of three single vaccines:

• There must be a gap of a month between each vaccine. This leaves children unprotected for a longer period.
• There is no scientific evidence that the single vaccines are safer than the MMR vaccine.
• Due to the vaccines having to be given on three separate occasions, one or more of the vaccines are likely not to be given to the child.

Summary

The MMR vaccine has resulted in a significant reduction in the incidence of measles, mumps and rubella - three serious diseases. Ultimately, the decision as to whether a child should be vaccinated lies with the parents, who should take into account the benefits and possible risks associated with the vaccine before reaching a decision.