Introduced to the UK in 1988, the MMR vaccine protects against three viruses: measles, mumps and rubella. These viruses cause disease and can lead to severe complications in infected individuals. Until recently, the MMR vaccination program had practically wiped out all three; however, a scare surrounding a now-discredited clinical trial means that the diseases are now infecting unprotected children once more.

The vaccine consists of 'attenuated' live organisms, meaning that the organisms are weakened and thus are not infectious, though they can cause some very mild symptoms. At the time of writing, the UK vaccination schedule includes two doses of MMR, one at 13 months and one at least a month later but before school age. The vaccination can be given by injection into an upper arm, thigh or buttock muscle.

This entry looks at the diseases the vaccine prevents, and then looks at some of the issues surrounding the vaccine.

Measles

As with all three viruses mentioned in this entry, the measles virus is spread by water droplets produced by coughs and sneezes. While a characteristic rash appears around four days after infection, there may be earlier, non-specific signs such as a fever, cough, loss of appetite and conjunctivitis (red, painful eyes). A previously-well child with measles will usually have to spend a week in bed and will be unable to return to school for several days after the rash has gone. The disease is more severe in affected adults.

One in 15 of all infected children will also develop serious complications such as pneumonia, middle ear infection, convulsions, encephalitis (brain swelling) and death. Links have also been made between measles infection and the development of various autoimmune diseases. Very rarely, a child will go on to develop subacute sclerosing panencephalitis (SSPE), a fatal disease that can follow seven or more years after infection with measles.

In the year before MMR vaccination was introduced, the measles virus infected 86,000 children, 16 of whom died. It is estimated that without the vaccine, the UK would see around 600,000 cases per year (including around a hundred thousand children), and between 50 and 100 would die from either encephalitis or pneumonia.

Meanwhile, measles continues to kill 1.5 million children each year worldwide, and there is strong evidence that the virus increases the usage of vitamin A, thus leading hundreds of thousands of malnourished third world children to become blind each year.

Mumps

The mumps virus typically causes swelling of the parotid glands, which are situated just in front of the ears. The earliest signs of infection are non-specific and include malaise, fever, headache, flu-like symptoms. A third of individuals infected with mumps are completely unaffected.

However, there are a number of serious complications of infection such as meningitis, encephalitis (brain swelling), and hearing loss. The rate of complications is higher after puberty, with another rare complication being inflammation of the testicles or ovaries, with a small risk of permanent infertility.

In the year before MMR vaccination was introduced, the mumps virus produced around a thousand hospitalisations and five patients died.

Rubella

Rubella usually causes a mild infection in young children, causing a short-lived rash and fever along with a cough, sore throat, swollen glands, and malaise. Complications include arthralgia (joint pains), arthritis, encephalitis (brain swelling) and ITP (immune thrombocytopenic purpura - a bleeding disorder).

Most important, however, is the damage that the rubella virus can do to an unborn child if the mother is infected. Congenital rubella syndrome occurs in 90% of mothers who are infected during the first ten weeks of pregnancy, and may also cause damage at any time during the first trimester. The syndrome leads to deafness, blindness, growth retardation, heart defects and brain damage. Both mumps and rubella may also cause spontaneous abortion.

In the year before MMR vaccination was introduced, around 40 babies were born with congenital rubella syndrome.

Why Vaccinate?

As if the need to protect a child from the above nasties weren't enough, there's another reason to ensure as much of the population is vaccination as possible. If a sufficiently high proportion of a group of people are vaccinated against a disease, 'herd immunity' is achieved. This results in a dramatically reduced risk of exposure to infection for any unvaccinated individuals or those people where the vaccine hasn't resulted in full immunity.

Herd immunity also protects those whose immune systems aren't functioning and are at the greatest risk – for example, children with transplanted organs who are given immunosuppressant drugs or those born with immunodeficiencies. These two groups of children cannot be vaccinated and, if they are infected by one of the viruses, will almost certainly die. If achieved, herd immunity greatly reduces this risk.

Achieving herd immunity is quite a big matter – it greatly reduces the danger posed by a disease, as unvaccinated individuals are too few and far between to sustain the infection¹. This is vital as, without herd immunity, a vaccination program can simply delay infection in the unvaccinated individuals instead of preventing it. The figure required for herd immunity against measles is 95%.

Why Give the Vaccine Twice?

Despite its amazing success (see below), the MMR vaccine isn't 100% effective. After the first dose, 90% of children will be immune to measles for life, with rates of 85% for mumps and 98% for measles. For those who aren't immune after the first dose, the second dose is sufficient to make almost every child immune. The second dose also boosts the immunity of those who responded to the first dose.

Side Effects of the Vaccine

Like all live vaccines, the MMR vaccine has a number of predictable side effects. These include a slight soreness, redness and swelling around the injection site due to a slight immune reaction to components of the vaccine, or a mild measles rash (one in ten) or fever (one in 15) a week after the injection. One in 50 children will go on to have a mild episode of mumps around three weeks after the injection.

There are also some more severe side effects of the vaccination. These are listed below, and their rates are compared to the rates found in unvaccinated children who catch measles.

• Febrile convulsions²
  • After vaccine: 330 per million
  • With measles: 2-5,000 per million
• ITP³
  • After vaccine: 35 per million
  • With measles: 330 per million
• Anaphylaxis⁴
  • After vaccine: 1-10 per million
  • With measles: 0 per million
• Encephalitis⁵
  • After vaccine: 1 per million (equal to the background rate)
  • With measles: 200-1,000 per million

Clinical Reasons Not to Vaccinate

Severe reactions: the vaccine contains ingredients that can cause allergic reactions, and so a genuine severe allergic reaction to a dose of MMR (as opposed to the mild side effects mentioned above) precludes a second dose. While the original measles vaccine was produced using eggs, the modern MMR vaccine does not contain any egg proteins and is now considered safe for use in those with egg allergies. While it used to be a common practice to admit those with egg allergies to hospital to have the MMR, this practice is dying out.

Acute illness: previous reasons for this included concerns that the vaccine wouldn't take, or that side effects would be more severe. However, the actual reason for not giving vaccines to acutely ill individuals is to avoid the vaccine being blamed if the illness naturally becomes worse.

Pregnancy: doctors tend to avoid giving any form of medication to pregnant women unless absolutely necessary.

Immunosuppression: apart from the fact that a good immune system is needed in order to form antibodies, the vaccine is live attenuated and so should not be given to those with a suppressed immune system due to either medication or disease. The exception is individuals with HIV who are yet to develop symptoms of immunosuppression.

Does the Vaccine Work?

Before the introduction of the original measles vaccine during the 1960s, there were around 460,000 cases in England and Wales each year. The measles vaccine led to a sharp decline in the disease and, with the introduction of the MMR in 1988, the rate of measles infection was further reduced and the rates of mumps and rubella also fell dramatically. The following compares the number of preventable infections in the years just before vaccination with those in 2003:

• Measles
  • Pre-vaccination: 460,407 cases
  • 2003: 2,488 cases
  • Change: down by 99.99%
• Mumps
  • Pre-vaccination: 20,713 cases
  • 2003: 4,204 cases
  • Change: down by 79.7%
• Rubella
  • Pre-vaccination: 24,570 cases
  • 2003: 1,418 cases
  • Change: down by 94.22%

However, with the drop in vaccination uptake due to the scare in 1998, the number of cases has begun to rise again, with 2006 seeing the first measles death in the UK for 14 years, followed by another in 2008. At the time of writing (2008), measles is widespread in the population and it is estimated that three million children have missed either one or both of their MMR vaccinations.

Anti-vaccine Campaigners

For a number of reasons, there are people who do not think that vaccines such as the MMR vaccine are safe. This may be due to bad publicity about vaccinations, a philosophical objection to vaccinations or, very occasionally, concern about the payments that GPs (general practitioners or family doctors) receive for meeting immunisation targets. Alternatively, there may be a belief that the diseases are not very significant or that immunity via antibodies obtained naturally after surviving the disease is preferable to the vaccinations.

The Autism Scare

In 1998, Dr Wakefield published a study in The Lancet detailing the investigation of 12 children who had attended a bowel clinic at the Royal Free Hospital in London. All 12 had bowel abnormalities, and ten of them were suspected to have autistic spectrum disorder, a disorder affecting a person's ability to communicate and socialise while also having effects on learning in those with low-functioning autism.

During the late 20th Century and early 21st Century, the rate of diagnosis of autism has steadily been increasing, and Wakefield started to compare this with the onset of the MMR vaccination program. Wakefield sent all 12 children for a barrage of tests and then came up with a link between the MMR vaccine, which they had been given at 13 months old, and a disease he called autistic enterocolitis – a combination of bowel problems and autistic regression.

Wakefield's claim of a link between the MMR vaccine and 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 1995, 92% of children were covered by the vaccine, whereas only 85% were covered at the time of writing (2008).

Wakefield's trial has since been discredited by The Lancet. At the time of writing, Wakefield and two of his colleagues are facing a fitness-to-practice investigation by the General Medical Council. The charges against them include unethical treatment of children used in the study, with lumbar punctures and colonoscopies being performed regardless of whether they were necessary, and dishonesty, on the basis that Wakefield refused to reveal why he chose particular children for the study. It is also claimed that Wakefield had a serious conflict of interests, with his study having been supported by parents who sought to sue for damages to their children that they claimed were due to the vaccine.

The View of the Scientific Community

Among scientists⁶, there is a widespread belief that this link is not present for five main reasons:

• The original study that suggested the link to autism included only 12 children. For a study of the the type that Wakefield performed to be scientifically sound, it would have to consist of thousands of patients and be repeatable by independent scientists. Neither was the case.

• The study was retrospective – parents with autistic children were found and surveyed up to eight years after vaccination – and lacked a control group – a group of children who were studied but not vaccinated would have been a suitable control group.

• 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. A total of 537,303 children were involved, of which 440,655 were immunised. No increased risk of autism was found for those who were immunised compared to those who were not⁷.

• 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. Furthermore, the removal of the MMR vaccine in Japan had no effect on the increasing rate of diagnosis of autism⁸. A number of trials have also shown that the removal of thiomersal (aka thimerosal), a mercury-containing preservative thought to cause autism, has not slowed the increasing rate of diagnosis of autism.

• It is frequently stated that a child developed autism soon after the MMR vaccine. However, autism is always first recognised by parents between 15 and 24 months of age, regardless of whether the vaccine is given⁹. 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.

Despite strong evidence that there is no link between the MMR vaccine and autism, it is impossible to absolutely rule it out. Science by its nature is based on a theory being created to explain the available evidence, new evidence being found that isn't explained by the theory and a better theory being established. All that can be said is that the risks, if they do exist, are far outweighed by the benefits of the vaccine.

The Possibility of Separate Vaccinations

Wakefield suggested the use of individual vaccines as a safer alternative. At the time of writing, around 5% of parents request these from their doctors despite strong evidence against the link between the triple vaccine and autism. In fact, the use of only the triple vaccine in the UK means that single vaccines are untested, and there is no evidence that they would be any less likely to cause problems than the triple vaccine. Furthermore, the use of three separate vaccines would mean a delay in protecting children as gaps would have to be left between vaccinations, and there would be an increased risk of the child missing one or more of the vaccinations.

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, both to their own child and the population at large, as well as the possible risks associated with the vaccine, before reaching a decision.

Please Note: h2g2 is not a definitive medical resource. If you have any health concerns you must always seek advice from your local GP. You can also visit NHS Direct or BBC Health Conditions.