Background
This analysis is based on an older version of our inference model which is accurate but more difficult to read

Question

Does the MMR (measles, mumps, and rubella) vaccine cause autism?

Hypotheses
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Calculated Conclusions
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Conclusions
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1

99.9%
No autism:

The MMR vaccine does not cause autism.

99.9%

2

0.09%
Conspiracy:

The MMR vaccine does cause autism in a measurable number of cases, and the health organizations and pharmaceutical companies are deliberately covering it up.

0.09%

3

0.01%
Not established:

The MMR vaccine does cause autism in a measurable number of cases, but the health organizations and pharmaceutical companies haven't established this causal relationship yet.

0.01%

Summary

The number of autism cases has increased significantly in the past few decades, from approximately 1 in 2,500 children in 1966 to 1 in 68 in 2016. The increase in the number of autism cases is attributed in part to improved screening and broadening of the diagnostic criteria.

The alleged association between the MMR (measles, mumps and rubella) vaccine and autism began in 1998, when Andrew Wakefield and several coauthors published a research paper in The Lancet, a leading British medical journal, suggesting a link between them. Wakefield's findings caused great concern among parents in the UK and the US and led to a significant drop in vaccinations of children. Numerous subsequent studies have failed to support an association between the administration of the vaccine and autism spectrum disorder. Beginning in 2004, British investigative journalist Brian Deer wrote several articles accusing Wakefield of concealing conflicts of interest, manipulating evidence, and other unethical research practices. In 2010 The Lancet retracted Wakefield's study after several elements in the study were found to be "incorrect, contrary to the findings of an earlier investigation."

Another study (from 2003) reported elevated levels of measles antibodies in children with autism, which could indicate a link to the vaccine. However, four subsequent studies failed to find such a correlation. This inconsistency seems to indicate that the first study had some methodological error.

These two studies were the only studies to suggest a link between the vaccine and autism, while many studies by different organizations consistently fail to find such a relation.

When considering all the studies together, along with evidence such as an increase in autism cases in Japan following the termination of MMR vaccinations, the analysis concludes that it is extremely unlikely that the vaccine causes autism.

Another explanation for the evidence is that there is a broad, international conspiracy to cover up a link between the vaccine and autism (the “Conspiracy” hypothesis). A cover-up of this kind would require a massive conspiracy involving scientists, government agencies and pharmaceutical companies around the world. The analysis finds such a cover up to be very unlikely when compared to known past cover ups (like the conspiracy to hide the health risks associated with smoking), as it would involve a much larger number of organizations, many of which have little motivation to participate in such a conspiracy.

Note: The likelihood values that support the "Conspiracy" and "Not established" hypotheses have been estimated generously, since both are exceedingly unlikely hypotheses, yet considered by many to be plausible explanations. By inflating the estimates for the least likely hypotheses, we provide a wide margin of error and ensure that the conclusion is correct even if some evidence or data is missing from the analysis.

Note to Parents: This analysis measures the probability that the MMR vaccine can cause autism, even if rarely. The probability of 0.1% does not mean a 1 in 1000 chance of a child becoming autistic! It means that the evidence for the MMR vaccine causing autism is no different from the evidence for any other substance (say, apple sauce) causing autism. This conclusion is a strong indication that parents should vaccinate their children.

Key Evidence
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Contribution
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1

According to a study of 95,727 children with older siblings, there is no association between receiving the MMR vaccine and autism, even when the child had an increased risk of developing autism because their older siblings were diagnosed with it.

Sources: Journal of the American Medical Association
No autism

57%

Conspiracy

42%

Not established

0.6%

No autism

57%

Conspiracy

42%

Not established

0.6%

2

Dr. Bernadine Healy, former head of the National Institutes of Health, said that health officials don't want to study the hypothesis that vaccines could be damaging to a small subset of children who are susceptible because they're afraid it would scare people. She says vaccines are safe to the majority of the public, but she thinks the question of the hypothesis that vaccines could be damaging to a small subset of children hasn't been completely answered yet.

Sources: CBS News
No autism

48%

Conspiracy

3.5%

Not established

48%

No autism

48%

Conspiracy

3.5%

Not established

48%

3

The MMR vaccine is approved by the FDA.

Sources: Food and Drug Administration
No autism

48%

Conspiracy

48%

Not established

4.8%

No autism

48%

Conspiracy

48%

Not established

4.8%

Combined contribution of 10 remaining elements.
No autism

41%

Conspiracy

58%

Not established

0.2%

Analysis

Evidence
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Starting Point (1 item)

Studies (8 items)

The incidence of autism in Japan gradually increased from 1988 to 1992, as MMR vaccination rates gradually decreased. The incidence of autism significantly increased after 1993 when the use of the MMR vaccine was discontinued.

Sources: Journal of Child Psychology and Psychiatry
No autism

36%

Conspiracy

33%

Not established

31%

No autism

36%

Conspiracy

33%

Not established

31%

Dozens of studies, performed in multiple countries by numerous researchers and including more than a million subjects, failed to support an association between the MMR vaccine and autism.

Sources: Clinical Infectious Diseases
No autism

47%

Conspiracy

47%

Not established

6%

No autism

47%

Conspiracy

47%

Not established

6%

Scenario A:

No, Andrew Wakefield did not fabricate or otherwise modify the reports of an association in time of 6.3 days (range 1–14) between the administration of the MMR vaccine and the onset of behavioral symptoms of developmental regression in eight out of the twelve children he studied.

Scenario B:

Yes, Andrew Wakefield fabricated or otherwise modified the reports showing an association in time of 6.3 days (range 1–14) between the administration of the MMR vaccine and the onset of behavioral symptoms of developmental regression in eight out of the twelve children he studied.

Image of Andrew Wakefield
Image of Andrew Wakefield
www.theguardian.com
No autism

30%

Conspiracy

35%

Not established

35%

No autism

30%

Conspiracy

35%

Not established

35%

Reported data from 1979 to 1999 on the incidence of Autistic Spectrum Disorder in the North East Thames region in England, indicates that there was a steady increase in the incidence of autistic spectrum disorders each year and no sudden change in the trend after the MMR vaccine was introduced in 1988. 

Sources: The Lancet
No autism

42%

Conspiracy

39%

Not established

18%

No autism

42%

Conspiracy

39%

Not established

18%

According to a study of 95,727 children with older siblings, there is no association between receiving the MMR vaccine and autism, even when the child had an increased risk of developing autism because their older siblings were diagnosed with it.

Sources: Journal of the American Medical Association
No autism

57%

Conspiracy

42%

Not established

0.6%

No autism

57%

Conspiracy

42%

Not established

0.6%

According to the paper Incidence of autism spectrum disorders: Changes over time and their meaning, there was a significant increase of autism in England from the 1960s to the 2000s.

Sources: Acta Paediatrica
No autism

32%

Conspiracy

34%

Not established

34%

No autism

32%

Conspiracy

34%

Not established

34%

Four studies conducted from 2006-2013 indicate that an abnormal immune reaction to the measles virus does not have a causal role in autism, while a fifth study done in 2003 points towards the existence of such a role.
Sources: Pediatrics, Journal of NeuroVirology, Disease in Childhood, In Vivo, Pediatric Neurology
No autism

30%

Conspiracy

39%

Not established

30%

No autism

30%

Conspiracy

39%

Not established

30%

MMR contains Thimerosal (a form of mercury).

No autism

Conspiracy

Not established

No autism

Conspiracy

Not established

Individual cases (2 items)

The National Vaccine Injury Compensation Program awarded financial damages to the family of Ryan Mojabi because he suffered from encephalitis within a certain time frame after receiving the MMR vaccine that is appropriate for compensation. Ryan's parents claimed that Ryan suffered from encephalopathy as a result of the MMR vaccine that led to the development of autism. 

Sources: United States Court of Federal Claims
No autism

33%

Conspiracy

33%

Not established

33%

No autism

33%

Conspiracy

33%

Not established

33%

In 2012, a labor court in Rimini, Italy ruled that Valentino Bocca's parents, who claimed that the MMR vaccine caused their son's autism, were to be paid compensation by Italy's Ministry of Health. This ruling was later overturned in an appeals court.
Sources: la Repubblica
No autism

33%

Conspiracy

33%

Not established

33%

No autism

33%

Conspiracy

33%

Not established

33%

Other evidence (2 items)

Dr. Bernadine Healy, former head of the National Institutes of Health, said that health officials don't want to study the hypothesis that vaccines could be damaging to a small subset of children who are susceptible because they're afraid it would scare people. She says vaccines are safe to the majority of the public, but she thinks the question of the hypothesis that vaccines could be damaging to a small subset of children hasn't been completely answered yet.

Sources: CBS News
No autism

48%

Conspiracy

3.5%

Not established

48%

No autism

48%

Conspiracy

3.5%

Not established

48%

The MMR vaccine is approved by the FDA.

Sources: Food and Drug Administration
No autism

48%

Conspiracy

48%

Not established

4.8%

No autism

48%

Conspiracy

48%

Not established

4.8%

Storyline Assumptions
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Assumptions that derive from the evidence above are presented and evaluated here for each hypothesis.
Storyline assumptions:
Likelihood given hypothesis
(including preceding assumptions)