With so much sense and nonsense about coronavirus, I set to the side an important MMR vaccine systematic review that I’ve been wanting to review for a few weeks. Well, it’s time to focus on that.
Ever since Mr. Andrew Wakefield published his fraudulent, and subsequently retracted, study that seemed to show a link between the MMR vaccine and autism spectrum disorder (ASD), the anti-vaccine crowd has embraced it as if it were a scientific fact. Of course, they ignore over 150 published scientific articles that show that there are, in fact, no links at all.
This Wakefield chicanery has spawned a cottage industry of other anti-vaccine zealots like Del Bigtree and his fraudumentary Vaxxed, Robert F. Kennedy Jr., Christopher Exley, Christopher Shaw, James Lyons-Weiler, Tetyana Obukhanych, and many others.
And now we have a new, large, impressive MMR vaccine systematic review that once again provides affirmative evidence that there are no links between ASD and the MMR vaccine. None.
A quick systematic review primer
At the top of the hierarchy of biomedical research are systematic reviews or meta-analyses (these are used interchangeably, though there are some differences discussed below), which is why this type of analysis of MMR vaccine research is so valuable.
A systematic review is a critical assessment and evaluation of all research studies that address the effect of pharmaceuticals, devices, standards of care, and other issues related to a particular clinical condition. A researcher who produces systematic reviews uses an organized method of collecting and analyzing a body of literature on a particular topic using a set of specific criteria.
A systematic review may examine the quality of research in each of the papers, describe the results qualitatively, and find bias and errors. A published systematic review usually includes a description of the findings of the collection of research studies. Many systematic reviews also include a quantitative pooling of data, which is called a meta-analysis. All meta-analyses are systematic reviews, but not all systematic reviews contain meta-analyses.
One of the most frequently cited sources of systematic reviews is the Cochrane Collaboration articles.
MMR vaccine systematic review
In a paper published (pdf) in April 2020 in the Cochrane Database Systematic Reviews, the authors examined a total of 51 studies with over 10 million children to assess vaccine effectiveness. Moreover, they included 87 studies with over 13 million to scrutinize any association between the MMR vaccine and a variety of adverse events, including autism spectrum disorder.
Although my article is going to focus on the data related to ASD, the Cochrane review is huge, over 419 pages with over 100 tables and graphs. I would have to write a million-word article to cover everything in it.
But there are a few points that very valuable to our understanding of the MMR vaccine:
- Vaccine effectiveness in preventing measles was 95% after one dose, and 96% after two doses.
- Effectiveness in preventing mumps was 72% after one dose and 86% after two doses.
- Effectiveness in preventing rubella was 89%.
- Effectiveness in preventing varicella (or chickenpox) for the MMRV vaccine is 95% in a 10-year follow-up.
Yes, the vaccine works.
- There is no evidence supporting an association between the MMR (or MMRV) vaccine and cognitive delay.
- No association with encephalitis or encephalopathy.
- No association with type 1 diabetes (discussed here).
- No association with asthma.
- No association with dermatitis/eczema.
- No association with hay fever.
- No association with leukemia.
- No association with multiple sclerosis.
- No association with gait disturbance.
- No association with bacterial or viral infections.
Since this is real research, and I know some anti-vaxxers will cherry-pick data, it’s important to review a few issues that may be related to the vaccine.
- There is evidence that there might be an association between aseptic meningitis and MMR vaccines that contain the Urabe and Leningrad-Zagreb mumps strains. There was no association between aseptic meningitis and MMR vaccines that contain the Jeryl Lynn mumps strain. The Urabe strain has been abandoned in most of the world, and the Leningrad-Zagreb strain is only used in Russia, Croatia, and India. In the USA and most developed countries, the Merck MMR vaccine only includes the Jeryl Lynn strain.
- The analyses supported an association between the MMR vaccines and febrile seizures, a relatively minor event that occurs after fevers. However, about 2-5% of children experience one or more cases of febrile seizures prior to the age of 5, irrespective of immunizations. Cochrane determined that the risk of vaccine-induced febrile seizures from the MMR vaccine is about 1 per 1700 to 1 per 1150 doses.
- The analyses also provided evidence that supported an association between MMR vaccination and immune thrombocytopenia (ITP), a disorder which can lead to bruising and excess bleeding. However, and this must be stressed, the risk of ITP after the MMR vaccines is smaller than after natural infection with any of the viruses. ITP occurs naturally in about 5 cases per 100,000 children per year, while it is estimated that ITP occurs in about 2.5 cases per 100,000 children after vaccination. In other words, the MMR vaccine may actually reduce the risk of ITP in children.
MMR vaccine and autism
Time to get to one small, but important, part of this MMR vaccine systematic review.
- In a cohort study of 1.2 million children the risk of ASD in unvaccinated children is 451 per 100,000 and in vaccinated children, 419 per 100,000, or about a 7% reduction in risk of ASD. Though the statistics probably don’t support this claim, this is better evidence than the anecdotes from anti-vaxxers – the MMR vaccine may actually lower the risk of ASD.
- In a cohort study of 93,000 children, the risk of ASD in both unvaccinated and vaccinated children was around 85 per 100,000.
- In a cohort study of 1,914 children, the risk of ASD in unvaccinated children was 12 per 1000, while it was 9 per 1000 in vaccinated children. However, the study authors thought that indication bias probably caused the protective effect.
Clearly, this MMR vaccine systematic review showed no difference in the risk of ASD between MMR vaccinated and unvaccinated children. None. If anything, the largest study showed a slight protective effect for the vaccine.
The authors of this Cochrane MMR vaccine systematic review concluded:
Existing evidence on the safety and effectiveness of MMR/MMRV vaccines support their use for mass immunisation. Campaigns aimed at global eradication should assess epidemiological and socioeconomic situations of the countries as well as the capacity to achieve high vaccination coverage. More evidence is needed to assess whether the protective effect of MMR/MMRV could wane with time since immunisation.
This is one of the largest, most detailed, most carefully analyzed systematic reviews that I’ve ever read for vaccines. They looked at every possible relationship between the MMR or MMRV vaccine and a whole list of adverse events, including autism spectrum disorder.
I would hope that a study this powerful would silence the critics of the vaccine and reassure parents. We can only hope!
- Retraction–Ileal-lymphoid-nodular hyperplasia, non-specific colitis, and pervasive developmental disorder in children [retraction of: Wakefield AJ, Murch SH, Anthony A, Linnell J, Casson DM, Malik M, Berelowitz M, Dhillon AP, Thomson MA, Harvey P, Valentine A, Davies SE, Walker-Smith JA. Lancet. 1998 Feb 28;351(9103):637-41]. Lancet. 2010;375(9713):445. doi:10.1016/S0140-6736(10)60175-4
- Di Pietrantonj C, Rivetti A, Marchione P, Debalini MG, Demicheli V. Vaccines for measles, mumps, rubella, and varicella in children. Cochrane Database Syst Rev. 2020;4(4):CD004407. Published 2020 Apr 20. doi:10.1002/14651858.CD004407.pub4
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