I know this is old news – or at least it should be – but it bears repeating, especially as we are in the midst of a resurgence of measles. There is no link between the mumps, measles, and rubella vaccine (MMR) and autism, or any neurological disorder. A new study confirms this lack of association. This should go a long way to reassure the vaccine hesitant that the MMR vaccine at least is safe and should not be avoided.

This is a Danish study, and the largest study of the MMR vaccine and autism to date – “657,461 children born in Denmark from 1999 through 31 December 2010, with follow-up from 1 year of age and through 31 August 2013.” They found:

During 5,025,754 person-years of follow-up, 6517 children were diagnosed with autism (incidence rate, 129.7 per 100,000 person-years). Comparing MMR-vaccinated with MMR-unvaccinated children yielded a fully adjusted autism hazard ratio of 0.93 (95% CI, 0.85 to 1.02). Similarly, no increased risk for autism after MMR vaccination was consistently observed in subgroups of children defined according to sibling history of autism, autism risk factors (based on a disease risk score) or other childhood vaccinations, or during specified time periods after vaccination.

Overall there was no association between getting the MMR vaccine and later being diagnosed with autism. Further, there was no correlation when looking specifically at children who have a sibling with autism, and therefore might constitute a susceptible subpopulation. Further still, there was no clustering of autism diagnosis following the MMR vaccine administration, as might be expected if there was a causal link. This is a very large study with an adequate study design, so that if there were any increased risk of developing autism from the MMR vaccine we should be seeing it in this data – and we don’t.

We were already there with existing data. We now have many studies in many different countries showing no correlation between the MMR and autism. The new data is really beating a dead horse, which is fine when showing a lack of a risk. You can never prove a zero risk, only set limits on how high a risk can be. So the more data we collect, the closer we push any remaining possible risk toward zero. Adding a new massive study to the MMR data is therefore welcome.

It’s also worth pointing out that there was never any reason to suspect that the MMR could cause autism or that there was any correlation. Fears were largely triggered by Andrew Wakefield’s fraudulent and now retracted study from 1998. Even at that time the evidence was leaning against an association, and the study inspired a new round of research which not only failed to replicated Wakefield’s findings, they clearly showed that the alleged link does not exist.

Of course antivaxxers are never deterred by reality. As with any pseudoscientific group, when their claims collapse they simply migrate over to a new claim, without ever admitting error or truly giving up on the original claim. They never admitted error with MMR, and will resurrect their fearmongering about it when they feel they can.

After MMR their big focus became thimerosal, which is a vaccine preservative in some vaccines (it was never in the MMR) that contains a small amount of ethylmercury. Again, there was never any reason to suspect that thimerosal caused any health problems, let alone autism. All the antivaxxers had was a general trend of increasing vaccine schedule and increasing diagnosis rates of autism happening at the same time (along, of course, with countless other things – see spurious correlations for examples). But again, scientists are happy to investigate any potential risk, especially to reassure the public.

Two decades of subsequent research has shown no correlation between vaccines in general or thimerosal specifically and autism or any neurodevelopmental disorder. Further, out of an abundance of caution and to limit total human exposure to mercury, thimerosal was removed from the routine vaccine schedule in the US in 2002. At the time antivaxxers predicted that autism rates would plummet – they never did. They kept trying to push back the time, saying that pediatricians still had stockpiles of old vaccine with thimerosal (even long past their shelf life). Claims kept getting more an more bizarre – the mercury in vaccines is being exactly replaced by mercury from coal burning, or the tiny dose in some flu vaccines (also on the wane) is enough to cause the full harmful effect (so – no dose response curve, even though that was the very basis of their original claims).

So here we are, 17 years later, thimerosal in the routine vaccine schedule is a distant memory, there is barely any in a shrinking subset of flu vaccines, and autism rates continue to rise – although they are starting to level off (which is what scientists predicted – at some point the diagnosis rates will start to match the true rates).

On that last point – the incidence of autism diagnoses has increased, but the evidence is pretty clear that this is due to an expanded diagnosis and increased efforts to diagnose autism, plus some diagnostic substitution. In fact, when consistent methods are used to estimate the true incidence of autism, the rates have been steady for the last two decades.

After the death of the MMR hypothesis, and the death of the thimerosal hypothesis, antivaxxers did not give up. They never do, because they are ideologues. For them it is always and forever about the vaccines. So they just move on to new claims, or just make vague claims about “toxins” without getting specific.

But for those who are interested in the science, the results are pretty clear. This new study adds to the pile showing that vaccines are safe and effective. What is a real hazard is misinformation about vaccines, causing well-meaning parents to avoid them, putting their children and society at risk for once-eliminated diseases. We all pay the price.