The MMR vaccine and autism

Claims that the MMR vaccine significantly increased the risk of developing serious neurological disorders were reported in four newspapers (1,3-5). However, the research study on which these claims were based had several flaws (6). Therefore the reliability of the reported relationship between MMR vaccination and neurological disorders such as autism should be questioned.

• The results of a study to analyse the incidence of neurological symptoms following MMR immunisation was reported in the Daily Mail (1) on 20 May 2003. The article in the Daily Mail appears to have been based in part on an article that was published in Pulse (2) on the 19 May 2003. The Independent (3), The Guardian (4) and The Sun (5) all reported the same story on 21 May 2003 after the research paper became publicly available.
• The research study in question was a retrospective comparative study that compared the incidence of severe neurological disorders in children vaccinated against measles, mumps and rubella (MMR vaccine) with children vaccinated against diphtheria, tetanus and whole cell pertussis (DTwcP vaccine) (6). The researchers reported an increase in the rate of severe neurological disorders in those given MMR compared with those given DTwcP. The researchers suggested that a killed form of MMR should be made available, or, if live MMR were to continue to be used, parents should be offered a choice of separate vaccinations.
• The newspapers accurately reported the researchers' conclusions. However, the study was flawed therefore the reliability of the reported relationship between MMR vaccination and neurological disorders such as autism should be questioned.

Evaluation of the evidence base for a link between the measles, mumps and rubella (MMR) vaccine and autism

Where does the evidence come from?

The research was conducted in the US by Mark R Geier from the Genetic Centers of America and David A Geier from MedCon Inc.

What were the authors' objectives?

The authors stated that their objectives were to analyse the incidence of serious neurological symptoms in a comparative examination between MMR vaccine and a DTwcP vaccine control group.

What was the nature of the evidence?

The evidence came from a retrospective comparative study that compared children who had been given the MMR vaccine, with children who had been given the DTwcP vaccine. The study covered the period 'from 1994 through 2000'. Data were obtained from the Vaccine Adverse Event Report System (VAERS) database. This is a US programme which collects information from reports of possible side effects that occur after the administration of vaccines (7). Estimates of the total number of children who received the MMR or DTwcP vaccines were obtained from the US Center for Disease Control (CDC).

What were the factors of interest?

The outcomes of interest in the study were serious neurological reactions that developed within 30 days of MMR immunisation. Comparison was made with children who had received the DTwcP vaccine.

What were the findings?

Twenty-nine boys and eight girls out of the 25 million children who had received the MMR vaccine were reported to have developed autism, an incidence of 1.5 for every million vaccinations. This compared with 0.29 cases per million children who had received the DTwcP vaccine. The incidence of cerebellar ataxia, mental retardation and permanent brain damage were also reported.

The authors reported that the mean age of onset of symptoms was 1.8 years and the mean interval between vaccination with MMR and onset of signs and symptoms of the disorders was 5 to 10 days. No equivalent information was given about the children vaccinated with DTwcP.

What were the authors' conclusions?

The authors concluded that the study showed a highly significant increase in serious neurological conditions following primary paediatric MMR vaccination in comparison to a DTwcP vaccine control group. The authors also suggested that a killed form of MMR should be made available, or, if live MMR were to continue to be used, parents should be offered a choice of separate vaccinations.

How reliable are the conclusions?

The study has several flaws, so the reported relationship between MMR vaccination and neurological disorders such as autism should be questioned.

Data were obtained from the VAERS database. This database provides information on children reported as having had an adverse reaction to a vaccine. It accepts reports of adverse events that may be associated with US licensed vaccines from health care providers, manufacturers, and the public. Doctors and other vaccine providers are encouraged to report adverse events, whether or not they believe that the vaccination was the cause.

The US Food and Drug Administration and CDC state that 'the report of an adverse event to VAERS is not proof that a vaccine caused the event. Some infants coincidentally experience an adverse event shortly after a vaccination. In such situations an infection, congenital abnormality, injury, or some other provocation may cause the event. Because of such coincidences, it is usually not possible from VAERS data alone to determine whether a particular adverse event resulted from a concurrent condition or from a vaccination - even when the event occurs soon after vaccination'. Given this, great care needs to be taken in analysing this type of data. If an analysis of VAERS data suggested a possible link between an adverse event and vaccination, this relationship would need to be further studied in a more rigorously controlled fashion. The research paper in question failed to do this.

The authors of the study justified their choice of control group, which consisted of children who received the DTwcP vaccine by saying that the incidence after vaccination were expected to be equal and that any limitations would apply equally to each group. However, they did not provide any evidence to support this assertion. While the average age of children in the MMR group was 1.8 years, no information on the age of children vaccinated with the DTwcP vaccine was given. It appears that the DTwcP schedule used in the US during the study period involved vaccination at two, four and six months (8). Since 1999, the CDC in the US has recommended that DTwcP be replaced by DTaP, which should be given to children of 16 months and over (9). If the data presented related to children aged six months or less, the comparability of the DTwcP and MMR groups must be questioned. The diagnosis of autism, for example, is commonly made around the age of two years - close to the average age of MMR vaccination. In addition, the changes in a child's developmental profile at an average age of 1.8 years are very different to those present in a child aged six months or less. Therefore the incidence without vaccine would be different at different ages, so age is a factor that a more rigorous study would have controlled for.

In addition, the reporting of serious neurological disorders may have been different for the two groups, which leaves uncertainty about the total incidence of serious neurological disorders in either group.

The authors suggested that a killed form of MMR should be made available, or, if live MMR continued to be used, parents should be offered a choice of separate vaccinations. Neither killed combined vaccination nor live separate vaccinations were investigated, their recommendation does not have a basis in the evidence presented.

Systematic reviews

Information staff at CRD searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic.

There were no related systematic reviews identified on the Cochrane Database of Systematic Reviews or on the Database of Abstracts of Reviews of Effects (DARE).

This report has been prepared for the National electronic Library for Health by the NHS Centre for Reviews and Dissemination, based at the University of York

References and resources

1. MMR raises risk of brain disorders say researchers. Daily Mail, 20 May 2003, p2.

2. Researchers claim vaccines cause nine out of 10 neurodevelopmental disorders. Pulse, 19 May 2003, p7.

3. Claim of MMR dangers dismissed as 'flawed'. The Independent, 21 May 2003, p11.

4. MMR study finds links to brain illnesses. The Guardian, 21 May 2003, p10.

5. MMR jab's 'new link' to autism. The Sun, 21 May 2003, p25.

6. Geier MR, Geier DA. Pediatric MMR vaccination safety. International Pediatrics 2003;18:108-113.

7. Food and Drug Administration. CBER - vaccine adverse event reporting system.
Available from: http://www.fda.gov/cber/vaers/what.htm. Accessed 22 May 2003.

8. CDC. Recommended childhood immunization schedule - United States, January-June 1996. Morbidity and mortality weekly report 1996;44:940-3.
Available from: http://www.cdc.gov/mmwr/preview/mmwrhtml/00039897.htm. Accessed 22 May 2003.

9. CDC. 1999 Recommended childhood immunization schedule.
Available from: http://www.cdc.gov/od/oc/media/fact/childimm.htm. Accessed 22 May 2003.

Consumer information

MMR - the facts

DoH - Measles, Mumps and Rubella Vaccine (MMR)

Health Education Board Scotland - MMR Information Centre

Previous Hitting the Headlines summaries on this topic

The MMR vaccine debate. Hitting the Headlines archive, 24 September 2001.

'MMR may be linked to autism'. Hitting the Headlines archive, 9 August 2001.

New study on MMR and autism. Hitting the Headlines archive, 7 November 2002.

Misreporting Measles Research. Hitting the Headlines archive, 6 February 2002.

What is the evidence for and against the MMR vaccine? Part 1. Hitting the Headlines archive, 7 February 2002.

What is the evidence for and against the MMR vaccine? Part 2. Hitting the Headlines archive, 7 February 2002.

Study finds no evidence of MMR and autism link. Hitting the Headlines archive, 12 June 2002.

Biggest study clears MMR jab. Hitting the Headlines archive, 12 January 2001.