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Measles, mumps and rubella - safety of the combined vaccine

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VOL: 100, ISSUE: 09, PAGE NO: 74

Helen Bedford, PhD, RGN, RHV, FRCPCH, MFPH, is lecturer in children's health, Centre for Epidemiology and Biostatistics, Institute of Child Health.

MMR is the combined measles, mumps and rubella vaccine. It is a live viral vaccine in which the viruses have been attenuated so that they cannot cause disease but are capable of provoking an immune response.

MMR is the combined measles, mumps and rubella vaccine. It is a live viral vaccine in which the viruses have been attenuated so that they cannot cause disease but are capable of provoking an immune response.

The combined vaccine was introduced in the US in 1972 and in the UK in 1988. It is given shortly after the child's first birthday. Antibodies acquired by the baby from the mother in utero may persist until the age of about 12 months and neutralise the effect of the vaccine, so it should not routinely be given earlier than this.

One dose of MMR will produce 90 per cent protection against measles, 85-90 per cent protection against mumps and 98-99 per cent protection against rubella (Edees et al, 1991). However, as the aim of the vaccine programme is to eliminate the three infections completely, even higher levels of immunity than this are needed. Since 1996 a second dose of vaccine has been recommended before school entry to provide protection for those who did not respond to the first dose.

The rates of seroconversion (the production of specific antibodies in response to an antigen-vaccine or virus) after the second dose are very high and adverse reactions are much lower (Virtanen et al, 2000). In countries with high uptake of two doses of MMR vaccine, the three diseases have become rare and they were eliminated completely from Finland in 1996 (Peltola et al, 2000).

History of MMR
From the early 1970s schoolgirls and susceptible adult women were offered the single rubella vaccine to ensure protection against rubella in pregnancy, which could result in congenital rubella syndrome in the baby.

Although highly successful in reducing both the number of cases of babies born with congenital rubella syndrome and terminations of pregnancy associated with rubella infection, this policy had no impact on circulating rubella infection.

The introduction of MMR

When MMR was introduced it represented a change in policy, particularly in the control of rubella.

When the combined vaccine was introduced in the UK it had already been used in other countries for some time and so there was considerable evidence, experience and research showing it to be highly effective and to have a good safety record.

In the UK parents were attracted to the idea of protecting their child against three infections with one vaccine and in one survey of over 3,000 parents, 60 per cent said they would prefer a combined MMR vaccine to a single measles vaccine (Peckham et al, 1989).

A single mumps vaccine was never used routinely in the UK and so MMR has provided additional protection against this infection.

Medical concern and media coverage
In 1998 a paper was published in The Lancet in which the authors described 12 children who had bowel inflammation as well as behavioural problems. Nine of the children were diagnosed as having autism (Wakefield et al, 1998). The authors suggested that they were describing a new disease.

The paper caused concern because the onset of the behavioural problems was reported by eight of the parents or GPs to be closely linked in time to the receipt of MMR vaccine. The authors concluded: 'We did not prove an association between measles, mumps and rubella vaccine and the syndrome described.'

However, public statements from one of the researchers and the subsequent media coverage this generated ignited parents' concerns. The researcher said that he had enough doubt in his mind over the safety of the vaccine to suggest that children should be immunised with the individual components at yearly intervals. This view is not supported by any scientific evidence and his fellow researchers have emphasised this. However, the suggestion raised concerns among parents and some health professionals.

The evidence

Since the paper was published a considerable amount of research has been conducted to investigate whether the MMR vaccine may cause the problems originally described. Concern has also been raised over a conflict of interest, which may compromise the original study.

In addition several expert groups in the UK and the US have reviewed all the evidence (Medical Research Council, 2001). The conclusion is that there is no evidence to support the suggestion that MMR causes autism and/or bowel disease, and that there is mounting evidence showing no such link. Despite this, some parents remain very scared and misguidedly believe that 'rather than take any risk at all', they should choose to go down the single-vaccines route.

MMR vaccine versus single vaccines
The evidence relating to MMR vaccine shows it to be highly effective and with a good safety record, and there is no evidence to support the use of single vaccines.

A regimen of single measles, mumps and rubella vaccines given separately at yearly intervals in very young children has never been used anywhere in the world. In view of this, it is of concern that many parents have failed to seek the same level of evidence for the safety and efficacy of single vaccines as they have for the MMR vaccine. There seems to be an acceptance among some parents that giving the single vaccines is in some way an inherently safer and equally effective option.

Problems associated with single vaccines

In fact, the use of single vaccines could have several harmful consequences. For example:

- One of the key principles of immunisation is that vaccines are given as early as possible to ensure protection before the age when infection is likely. Any interval between vaccine doses leaves individual children at risk while they wait for the next vaccine;

- Lower uptake is a real possibility, not only because of the practical difficulties of taking children for immunisation on six separate occasions but also because some parents may pick and choose which vaccines they want. This is particularly true of rubella and mumps;

- Giving children six separate injections when they only require two is unkind and not in their best interests.

Safety considerations with single vaccines

MMR continues to be recommended as the most effective way of protecting children. As a result single vaccines have not been made available on the NHS. However, in response to a demand from some parents, clinics have been set up to offer this option.

The vaccines offered in these clinics have been imported and are not licensed in this country. This means that the usual stringent checking procedures that are in place for any product licensed in the UK are lacking.

There have been concerns about the safety and efficacy of some single mumps vaccines that have been imported in the past and their importation has now been restricted (Moreton, 2003).

In addition there have been reports of poor standards of practice in single vaccine clinics (Department of Health, 2003).

Specific safety questions

All of these issues place parents in a very difficult position as they try to ensure that their child is receiving the best possible treatment. If parents are insistent on choosing single vaccines for their children they should seek answers to the following questions from the provider of the vaccine:

- What vaccines are their children being offered?

- Are there results showing the purity and potency of the vaccine being used?

- How has the vaccine been stored?

- What will be the interval between vaccines and what is the scientific evidence that supports such an interval?

- What follow-up for the child will be offered?

- When is the second dose of each vaccine scheduled to be administered?

Consequences of a fall in uptake
Uptake of MMR vaccine has fallen from 92 per cent in 1995 (Department of Health, 2003) to 79 per cent in 2003, with an even lower uptake in some areas.

Outbreaks of measles have already occurred and it has been reported that the size of these outbreaks indicate that the disease is once again close to becoming endemic (Jansen et al, 2003).

Recent outbreaks of mumps have so far been confined to adolescents and young adults who have had only one or no doses of MMR vaccine (Vyse et al, 2002) but these also pose a threat to inadequately protected younger children.

If rubella re-emerges among young children, congenital rubella syndrome will also reappear as some groups of childbearing women have high rates of susceptibility to the infection (Tookey et al, 2002).

Parents who express concern and who ask searching questions about this issue are only trying to do the very best for their children. It is important that health care professionals take these concerns seriously.

Parents value primary health care professionals as a source of information and advice on immunisation. They have a professional responsibility to keep well informed on this issue (Box 1) and, armed with this information, to spend time with parents answering their questions and allaying fears in an empathetic manner. This can be supported, if appropriate, with written information.

This article has been double-blind peer-reviewed.

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