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Even more on MMR

Measles vaccines and inflammatory bowel disease
Results
Autism, MMR and GP visits
Results
Comment

Previous issues of Bandolier ( 84 and 86 ) have addressed the safety of MMR vaccines, with strong evidence that there is no link between MMR and autism or between MMR and inflammatory bowel disease. But because concerns were so strong, it is valuable to return to the subject when even more powerful evidence concerning connections between MMR and childhood illness becomes available. Two more studies provide additional reassurance.

Measles vaccines and inflammatory bowel disease


This study [1] was conducted in the USA on the populations of four health maintenance organisations as part of a vaccine safety programme coordinated by the Centres for Disease Control and Prevention. In each of the HMOs trained medical abstractors reviewed medical records using a standardised instrument. Cases were individuals enrolled since birth (1958 was the earliest date) to 1989. Consistent criteria were used for definite and probable diagnosis of Crohn's disease, ulcerative colitis, or unspecified irritable bowel disease. This involved diagnosis by a gastroenterologist, with signs and symptoms and a diagnostic test for irritable bowel disease. Five controls were selected for each case, matched by sex, HMO and birth year. Dates of vaccination, type of vaccine, and date of diagnosis were also recorded.

Results


There were 155 cases of irritable bowel disease, with 152 definite or probable cases. Seven cases had no discernible onset date, two were of unspecified disease, and one was vaccinated when older than 10 years, leaving 142 cases and 432 controls for analysis.

Most had been vaccinated. Figure 1 shows the percentages vaccinated with MMR, with a measles-containing vaccine (MCV) or who were not vaccinated. The age at IBD diagnosis ranged from under five years to over 25 years (Figure 2).

Figure 1: Type of vaccine used


Figure 2: Age at diagnosis of IBD



The risk of inflammatory bowel disease was the same for vaccinated or unvaccinated people, split by type of vaccine or Crohn's disease or ulcerative colitis. There was an average of about 140 months between vaccination and diagnosis for cases and vaccination and control reference date for controls. Only 1% of cases developed inflammatory bowel disease within a year of vaccination and only 1% of controls developed inflammatory bowel disease within a year of vaccination.

Looking at whether children were vaccinated before 12 months, between 12 and 18 months, or after 18 months showed no difference in the risk of developing inflammatory bowel disease.

Autism, MMR and GP visits


A UK study examined the rates of GP consultation before and after MMR vaccination in children who became autistic and in controls [2]. It used the Doctor's Independent Network, a computerised database covering a million patients in 127 practices providing lifelong medical histories for children remaining with the practice from birth.

There were 79 cases with a diagnosis of autism, but one was immunised with MMR after autism was diagnosed, and seven were never immunised. That left 71 cases for analysis, with four controls chosen for each matched by age, sex, month of immunisation and practice.

Results


There was no difference in the number of visits in the two months (Figure 3) or six months (Figure 4) before or after MMR vaccination for cases or controls.

Figure 3: GP visits and vaccination - 2 months


Figure 4: GP visits and vaccination - 6 months



Comment


These are two excellent studies. They were both conducted on defined populations. They examined clinically important issues, either defined diagnosis of inflammatory bowel disease, or visits to GPs that could reflect a change in parental concern. In neither case was there any link with MMR vaccination.

One of the papers [1] has a superb discussion of methodological issues and history of the linkage between concern over MMR safety and the evidence. Both explain why the fears arose out of methodologically flawed studies.

Parents, and their physicians, can be reassured that high quality studies conducted around the world continue to demonstrate that there is no link between MMR and autism or inflammatory bowel disease. The weight of evidence on the safety of MMR is now rather large. The evidence in support of a link is incredibly weak.

A further thought is that there may just be the germ of an interesting paper or thesis in all this, examining the chronology of the scare in relation to the evidence available. There are lessons to be learned, certainly by news reporters, certainly by editors of learned journals and their peer reviewers, and probably by providers of healthcare. Disproving a negative is always going to be difficult, but knowing that good efficacy and safety assessment measures are in place for early warning is of major public importance.

References:

  1. RL Davis et al. Measles-mumps-rubella and other measles-containing vaccines do not increase the risk of inflammatory bowel disease. Arch Pediatr Adolesc Med 2001 155: 354-359.
  2. S DeWilde et al. Do children who become autistic consult more often after MMR vaccination? British Journal of General Practice 2001 51: 226-227.
  3. see also www.nap.edu
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