You should know, you're a medic: Is the MMR vaccine safe?

Carolyn Edwards explains why it is important for nearly all children to receive the MMR vaccine

See also The Press: Vaccination scaremongering

Media reports in 1998 of a possible link between autism, bowel disease, and the combined measles, mumps, and rubella vaccine (MMR) have made many parents question the vaccination. Understanding what their concerns are and being familiar with the current scientific evidence about the safety of MMR is important if doctors are to allay doubts about the vaccine.

Parents simply worry that MMR may cause autism or bowel disease. But the Department of Health, the World Health Organization, and medical establishments, such as the British Medical Association and the medical royal colleges, do not believe that MMR is linked to these conditions. They give several reasons.

What the evidence says

The Andrew Wakefield study¹ that sparked the MMR and autism scare has been widely criticised for several reasons. The study investigated only 12 children, nine of whom were diagnosed as being autistic. This sample is too small to make any claims regarding a possible connection between MMR and autism. About 600 000 children a year have been given the MMR vaccine in the United Kingdom since its introduction in 1988. The sample also had a strong selection bias. In eight cases the parents themselves had attributed their child's problems to MMR. Any apparent link between MMR and autism arises because the age when MMR is first given (12-15 months) coincides with the age when autism is first recognised.²

Secondly, independent expert reviews have found no good evidence to link MMR and autism. In March 1998, a Medical Research Council seminar, comprising 37 experts in virology, epidemiology, gastroenterology, immunology, paediatrics, autism, and child psychiatry, examined published and unpublished "evidence" for a link.³ They found no good evidence. Similar conclusions were drawn by a working party of the Committee for the Safety of Medicines.⁴ Its conclusions were based on a review of the medical records of 92 autistic children, released by a firm of solicitors representing parents who believed that their child had been damaged by MMR.

Thirdly, recent large scale studies have failed to support a link between MMR and autism.^5,6 One epidemiological study⁵ reviewed the medical records of all 498 known autistic children born in the North Thames region since 1979, covering the period before and after the introduction of the MMR vaccine. It found no difference in MMR vaccination rates between autistic chidren and those of the general population, no evidence that children vaccinated with MMR at younger ages developed autism earlier than children vaccinated later, and no clustering of autism development after vaccination. They also found that, although the number of cases of autism diagnosed has been rising since 1979, there was no sudden increase in the incidence of autism after the introduction of MMR. The increase in cases of autism since is 1979 is most likely due to changes in diagnostic criteria.

Common misconceptions

Many parents believe that giving the vaccines separately is safer than using the combined vaccination. Wakefield suggested that these vaccines should be given separately a year apart,⁷ although none of the Wakefield report's 12 other authors share this view. It is also commonly believed that the government uses MMR simply to save money, one vaccine being cheaper than three. In August 1999 the government banned the routine use of separate measles and mumps vaccines for several reasons. Firstly, there is no solid evidence that using separate vaccines is any safer than using MMR. Secondly, giving separate doses leaves children unprotected for a longer period. Thirdly, to be successful, national vaccination programmes must minimise the number of vaccinations given. Many children would inevitably miss one or more vaccinations if separate measles and mumps injections were given, leaving them open to infection.

In April, parental concern regarding MMR was refuelled by media reports of "compelling new evidence" for a link between MMR and autism.⁸ An unpublished study had apparently found evidence of the measles virus in the guts of 24 of 25 autistic children that may have come from the MMR vaccine. The Department of Health, however, dismissed the study as "unverifiable by usual scientific means" because it used a highly selective sample and inappropriate controls.

Know the real risks

Of course MMR does have side effects. For example, about one in six children develop a fever seven to 12 days after immunisation; about one in 3000 develop febrile seizures.⁹ These side effects are acknowledged by the medical profession, and in the majority of cases are benign. The benefits of MMR far outweigh the risk of these recognised side effects. Some parents mistakenly think that MMR is unsafe because it has some adverse effects. This is not the case. MMR has an excellent safety record. Hundreds of millions of children have safely received the vaccine world wide.

It is important that nearly all children receive MMR. Without a high uptake of the measles component, outbreaks of measles will occur, as seen recently in Ireland where two babies died.¹⁰ It is often forgotten that 1 in 1000 cases of measles are associated with encephalitis and 1 in 10 000 will die.

Carolyn Edwards, fourth year medical student, University of Leeds
Email: ugm7cae@leeds.ac.uk


studentBMJ 2000;08:303-346 September ISSN 0966-6494

1. Wakefield A, Murch SH, Anthony A, Linnell J, Casson DM, Malik M, et al. Ileal-lymphoid nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children. Lancet 1998;351:637-41.
2. Chen RT, Destefano F. Vaccine adverse events: causal or coincidental? Lancet 1998;351:611-2.
3. Department of Health. MMR vaccine is not linked to Crohn's disease or autism. Press release, 24 March 1998. http://www.doh.gov.uk.
4. Medicines Commissions Agency/Committee on Safety of Medicines. The safety of MMR vaccine. Current Problems in Pharmacovigilance 1999;25:9-10.
5. Taylor B, Miller E, Farrington CP, Petropoulos M-C, Favot-Mayaud I, Li J, et al. Autism and measles, mumps, and rubella vaccine: no epidemiological evidence for a causal association. Lancet 1999;353:2026-9.
6. Petola H, Patja A, Leinikki P, Valle M, Davidkin I, Paunio M. No evidence for measles, mumps and rubella vaccine-associated inflammatory bowel disease or autism in a 14-year prospective study. Lancet 1998;351:1327-8.
7. Birmingham K, Cimons M. Reactions to the MMR immunization scare. Nature 1998;4(5):478-9.
8. Measles jab: new link to brain damage. The Mail on Sunday, 9 April 2000.
9. Center for Disease Control Vaccine Information Statement, 16 December 1998. http://cdc.gov.nip/publications/VIS/vis-mmr.pdf
10. Measles outbreak feared. BBC News Online, 30 May 2000.