JUST days after a massive review concluded there is no evidence that the MMR vaccine causes autism or bowel disease come fresh claims from those who believe it does.
Earlier this year, John O’Leary’s team at Trinity College, Dublin, published claims that 75 out of 91 children with “regressive” autism had the measles virus in damaged areas of their bowels, whereas the virus was present only in 5 out of 70 normal youngsters. Now the group says that tests on 12 children randomly selected from the 75 measles-positive ones prove that the virus in their guts is the weakened strain used in MMR, the triple vaccine against measles, mumps and rubella. The findings will be presented next month to a meeting of the Pathological Society of Great Britain and Ireland.
The work was done to test the controversial theory of Andrew Wakefield that damage to the bowel caused by the measles vaccine allows bits of undigested proteins into the bloodstream, affecting the developing brain and leading to autism. “Showing MMR-derived virus [is present] in the damaged guts of autistic children adds to the evidence for a causal connection between MMR and autism,” Wakefield told 91av.
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But while the results support Wakefield’s theory, they don’t prove it. The gut problems could be a symptom rather than a cause of autism. Children with developmental problems may be unable to clear the virus from their bowels. Critics also point out that any harmful substances entering the blood should be filtered out before they reach the brain.
At a US Congressional hearing this week, Wakefield is expected to present further claims that more than 25 autistic children who’d had two MMRs (a pre-school booster is standard) had worse gut problems than those who’d had only one. The gut biopsies were analysed by researchers who were “blind to the children’s vaccine or developmental status”, he says. “This is simply a result you can’t fake.” The children’s behavioural symptoms were also more severe, Wakefield says.
But again, this doesn’t prove cause and effect. If some autistic children have problems clearing the measles virus, you’d expect their bowel problems to get worse on further exposure. And so far, no one has replicated any of the results. David Salisbury of Britain’s health department claims that the Irish group has refused to give other groups tissue samples so they can verify the findings.
What’s more, study after study has failed to detect any association between vaccination, bowel disease and autism. Last week, a review of no fewer than 2000 studies that will be published in Clinical Evidence concluded that MMR was safe. A similar review carried out last year by the Institute of Medicine in the US came to the same conclusion.
The failure to find any association, the institute stated, suggests that the worst MMR can do is cause bowel damage and regressive autism in a very few vulnerable children—so few that the effect is easily missed. Indeed, this is what Wakefield’s more cautious supporters believe.
But Wakefield goes much further. “You could attribute rising autism rates entirely to MMR interacting with some other factor which has been continually changing. MMR use has been steady for some time, but other variables during this period could link the vaccine and autism,” he told 91av. Wakefield thinks the increased incidence of autoimmune diseases and allergies, and past use of vaccines containing mercury, weaken the immune system, “skewing the way T cells respond, and leaving children vulnerable to MMR-induced damage”.
There certainly has been a rise in all kinds of autism, and the reasons for it are unclear. Yet unpublished data revealed to 91av (17 February 2001, p 17) suggest that rates of regressive autism—the kind of autism that would be caused by any environmental factor acting in early childhood—have not risen any faster than other forms of autism.
Critics say that in finding fault with the ever-growing list of studies that fail to find a link with autism, Wakefield is increasingly clutching at straws. Will anything convince him that he’s wrong? “The failure of a measles antiviral drug to prevent or reverse MMR-induced damage would certainly make me wonder,” he says. Such a drug, unfortunately, doesn’t yet exist.
A few senior figures in Britain’s medical establishment, who are reluctant to speak publicly, do ask awkward questions off the record. “Why look for other reasons to explain rising autism rates before ruling out MMR?” one asked 91av.
Other scientists, such as Elizabeth Miller of Britain’s Public Health Laboratory Service, argue the evidence that MMR is safe is so overwhelming that there’s no point in spending money on further research. But that won’t wash with the many parents who are still refusing to let their children have the MMR.