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Published: December 1999

MMR Vaccine Not Associated with Bowel Disease & Autism

Prescriber Update 19: 37-39
December 1999

Medsafe Editorial Team

The evidence continues to be contrary to there being an association between MMR vaccine and inflammatory bowel disease or autism.
One population-based study found that at age 2, vaccine coverage did not differ significantly for those with and without autism. Further, no association was found when the data were analysed for age at vaccination and diagnosis, and for clustering of developmental regression. Another study found exposure to measles infection in utero did not result in the development of Crohn’s disease later in life. In a third study gastrointestinal symptoms lasting > 24 hours and occurring from 20 hours to 15 days after vaccination were not a predictor of autism or inflammatory bowel disease. It had previously been postulated that vaccination caused bowel abnormalities through measles infection which increased absorption of non-permeable peptides which in turn resulted in developmental disorders.
The value of vaccination against measles infection is illustrated by the estimated 90-95% reduction in the number of cases of measles by the immunisation campaign to counter the NZ epidemic in 1997.

Evidence does not support alleged association

A small case series1 published by Wakefield et al in January 1998 suggested a link between MMR vaccine and autism and generated a flurry of media activity discrediting the vaccine. It was proposed that the vaccination caused bowel abnormalities through measles virus infection which increased the absorption of non-permeable peptides which in turn resulted in developmental disorders. In particular the association was thought to be with measles vaccine with perhaps the risk heightened by combination with vaccine components against mumps and rubella. A Prescriber Update article 2 was published in April 1998 presenting the current evidence that there was no association between MMR vaccine and either autism or inflammatory bowel disease. The present article is an update on this subject. The most recent data confirm the earlier contention that there is no association.

Vaccine coverage similar for 2-year-olds with and without autism

One population-based study3 found no association between MMR vaccine and autism, whichever way the data were analysed. Taylor et al identified children with autism born since 1979 from special needs registers in the North Thames district of the UK, and the child health computing system was checked for data on immunisation with MMR vaccine. 498 cases of autism were identified and 293 of these were confirmed by the ICD10 classification. There was a steady increase in cases of autism over time, but no change in the trend occurred in association with the introduction of MMR vaccine. Age at diagnosis did not differ for those vaccinated before or after 18 months and for those given no vaccination. At age 2 years vaccine coverage for those with autism did not differ significantly from that for children in the same birth cohort in the region. Developmental regression was not clustered in the months following vaccination.

Exposure to measles in utero not associated with IBD

A key study4 making an association between early exposure to measles virus and Crohn’s disease used a Swedish cohort of 25,000 babies born from 1940-1949. Four babies in this cohort were exposed to measles in utero, and three of these later developed Crohn’s disease. A more recent study5 identified 33 pregnant women who had been admitted to a Danish hospital with measles. Of the 22 offspring who were identified and who survived to adulthood, none was registered in a hospital or disease register with Crohn’s disease or inflammatory bowel disease. Hence, despite the larger exposed group than in the earlier study, no cases were found suggesting the earlier result was a chance event.

GI symptoms post-vaccination not a predictor of autism

For most of the children in Wakefield’s case series1 the symptoms of autism were identified 1-14 days after vaccination with MMR. The autism was thought to be associated with chronic measles infection of the bowel. Hence, Peltola et al6 followed up 31 cases of gastrointestinal symptoms occurring for > 24 hours in Finnish children who had received MMR vaccine. The gastrointestinal symptoms were reported as part of a national adverse events surveillance programme which aims to receive reports of all severe adverse events following vaccination. The time from vaccination to onset of symptoms was 20 hours to 15 days. The median duration of follow-up was 10.6 years. During this time no child developed autism and no evidence of association with inflammatory bowel disease was found. This study may have been limited by incomplete recording of cases. Nevertheless, because it was conducted on a population basis, the study is not subject to the selection bias of Wakefield’s case series.

The evidence continues to be contrary to there being an association between MMR vaccine and inflammatory bowel disease or autism. It is important that public confidence in vaccination is not undermined by an overemphasis on an hypothesised rare adverse outcome, without due regard for the benefits.

1997 immunisation campaign reduced measles cases by 90-95% in NZ epidemic

The value of vaccination is illustrated by the results7 of the immunisation campaign to counter the predicted New Zealand measles epidemic in 1997. Although the epidemic began before the campaign, the immunisation programme is estimated to have prevented 90-95% of cases. During a previous measles epidemic in 1991, 7 deaths and 10 cases of measles encephalitis occurred. In the 1997 epidemic there were no deaths and only one case of measles encephalitis.

References
  1. Wakefield AJ, Murch SH, Anthony A, et al. Ileal-lymphoid-nodular hyperplasia, non-specific colitis and pervasive developmental disorder in children. Lancet 1998;351:637-41.
  2. Mansoor O MMR vaccine, bowel disease and autism. Prescriber Update No.16, Apr 1998, p.41-2.
  3. Taylor B, Miller E, Farrington CP, et al. Autism and measles, mumps and rubella vaccine: no epidemiological evidence for a causal association. Lancet 1999;353:2016-29.
  4. Ekbom A, Daszak P, Kraaz W, et al. Crohn’s disease after in utero measles virus exposure. Lancet 1996;348:515-7.
  5. Nielsen LLW, Nielsen NM, Melbye M, et al. Exposure to measles in utero and Crohn’s disease: Danish register study. BMJ 1998;316:196-7.
  6. Peltola H, Patja A, Leinikki P, et al. 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. Mansoor O, Blakely T, Baker M, et al. A measles epidemic controlled by immunisation. NZ Med J 1998;111:467-71.

 

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