Vaccines and Autism: Over a Million Children Studied, No Link Found

Vaccines do not cause autism. The idea has been tested in well over a million children in Europe, North America and Asia, and every large, well-designed study has reached the same answer. The scare began with a retracted 1998 paper about 12 children. Its harms have fallen on children left exposed to measles, and on autistic people, cast for almost three decades as the outcome to be feared.

If you are a parent who has worried about this, you have not been foolish. The fear began with a paper in a respected medical journal and has been repeated by public figures ever since, and when the first signs of autism appear around the age routine vaccines are given, the timing can feel like evidence. This page sets out what researchers found, how the claim began and fell apart, and what it has cost, including to autistic people themselves.

Over a million children, many countries: no link to autism

The strongest evidence comes from whole-population studies that compare vaccinated and unvaccinated children across an entire country. A 2002 study of all 537,303 children born in Denmark from 1991 to 1998, 82% of whom had had MMR, found an adjusted relative risk of autistic disorder of 0.92 (95% confidence interval 0.68 to 1.24), where 1.0 means no difference. Age at vaccination and time since vaccination made no difference either^[5]. A 2019 study of the next 657,461 Danish children, born from 1999 to 2010, recorded 6,517 autism diagnoses and found a fully adjusted hazard ratio of 0.93 (0.85 to 1.02) for vaccinated compared with unvaccinated children^[2].

A 2014 meta-analysis pooled five cohort studies (1,256,407 children) and five case-control studies (9,920 children). The cohort data showed no relationship between vaccination and autism (odds ratio 0.99, 0.92 to 1.06), and none for MMR, thiomersal or mercury specifically; the case-control data agreed^[6]. The Cochrane review of MMR, drawing on 138 studies with 23,480,668 participants, found no evidence of an association with autism: rate ratio 0.93 (0.85 to 1.01), from two studies of 1,194,764 children, rated moderate certainty^[7].

Estimates slightly below 1.0 do not mean vaccines protect against autism, and the researchers do not claim so. The results cluster around “no difference”, with narrow ranges in the largest studies.

Studies built to find a hidden risk found none

The claim has been reshaped many times. Each version has been tested directly.

• The timing. Vaccines and the first signs of autism both arrive in early childhood, so “a temporal link between the two is almost predestined”^[8]. A UK study of 498 autistic children found no “step-up” in autism after MMR was introduced in 1988, and no clustering of developmental regression after vaccination^[9]. The 2019 Danish study found no clustering of autism cases after vaccination either^[2].
• A natural experiment. The Japanese city of Yokohama stopped giving MMR in 1993. In one ward of about 300,000 people, autism diagnoses among children did not fall; they rose, most sharply from the 1993 birth cohort^[10].
• “Susceptible” children. Among 95,727 privately insured US children with older siblings, those with an autistic older brother or sister were at no greater risk after MMR: the adjusted relative risk of autism by age 5 for two doses compared with none was 0.56 (0.31 to 1.01)^[11]. The Danish study agreed^[2].
• Ingredients. Thiomersal, a mercury-based preservative, showed no association in the 2014 meta-analysis (odds ratio 1.00, 0.77 to 1.31)^[6]. In 1,224,176 Danish children, aluminium from vaccines in the first two years was not linked to higher rates of any of 50 long-term conditions, including neurodevelopmental conditions such as autism and ADHD (hazard ratio 0.93 per extra milligram, 0.90 to 0.97)^[12].
• “Too many, too soon”. In a US study of 256 autistic and 752 comparison children, each 25-unit increase in the vaccine antigens a child had received by age 2 had an adjusted odds ratio for autism of 0.999 (0.998 to 1.001): no relationship at all^[13].

Every major expert review has reached the same conclusion

In 2004 the US Institute of Medicine concluded that “the body of epidemiological evidence favors rejection of a causal relationship between the MMR vaccine and autism”, and reached the same conclusion for thiomersal-containing vaccines^[14]. The Cochrane reviewers concluded that the evidence supports using MMR for mass immunisation^[7]. At its meeting on 27 November 2025, the World Health Organization’s Global Advisory Committee on Vaccine Safety reviewed 31 studies published from January 2010 to August 2025, together with the evidence on aluminium adjuvants including the Danish aluminium study, and reaffirmed its conclusions of 2002, 2004 and 2012: “vaccines, including those with thiomersal and/or aluminum, do not cause autism”. WHO published the finding on 11 December 2025^[1].

Families may have read otherwise. In November 2025 the US Centers for Disease Control and Prevention revised its web page on the subject; the page now says: “The claim ‘vaccines do not cause autism’ is not an evidence-based claim because studies have not ruled out the possibility that infant vaccines cause autism”^[15]. More than 30 autism and disability organisations, among them the Autistic Self Advocacy Network and other autistic-led groups, replied: “This is false”^[16]. No study can prove an effect of exactly zero, for vaccines or anything else; large studies show whether any effect is big enough to find. As UK researchers put it in 1999, if an association exists, “it is so rare that it could not be identified in this large regional sample”^[9]. The far larger studies since have found nothing either.

The claim began with 12 children and a paper that was later retracted

In February 1998 The Lancet published a paper by Andrew Wakefield and colleagues describing 12 children referred to a London gastroenterology unit with bowel symptoms and loss of skills. Parents of eight linked the start of symptoms to MMR^[3]. A case series of 12 children cannot show that a vaccine causes anything, but the paper and the publicity around it turned many parents against MMR^[17].

On 28 January 2010, after a hearing that had begun in July 2007, the UK General Medical Council’s Fitness to Practise panel handed down its findings of fact^[18]. As the Canadian Medical Association Journal reported, the panel found that the children, described in the paper as “a consecutive series”, had been carefully selected; that some of the research was funded by lawyers acting for parents suing vaccine manufacturers; and that Dr Wakefield had shown “callous disregard” for the children, on whom invasive tests were performed^[17]. In February 2010 The Lancet retracted the paper, saying that “several elements” of it “are incorrect, contrary to the findings of an earlier investigation”^[4][17]. In May 2010 the panel found Dr Wakefield guilty of serious professional misconduct and ordered that his name be erased from the medical register; he abandoned his appeal^[18]. In 2011 the BMJ published an editorial headed “Wakefield’s article linking MMR vaccine and autism was fraudulent”^[19].

A co-author, Professor John Walker-Smith, won his appeal in 2012, when the High Court quashed the findings against him, citing “inadequate and superficial reasoning” by the panel. That ruling concerned him alone, and the judge was clear about the science: “There is now no respectable body of opinion which supports his hypothesis, that MMR vaccine and autism/enterocolitis are causally linked”, he wrote of Dr Wakefield^[18]. Bowel symptoms in autistic children are real and deserve care (see autism and gut health), but they are not evidence that vaccines cause autism.

What the myth has cost: falling vaccination and the return of measles

In England, MMR coverage by the second birthday was 80% in 2003–04; the rise to 81% the following year was, in the official words, “the first year-on-year increase since 1995–96”^[20]. The High Court judge later described the “predictable adverse effect” of Dr Wakefield’s statements and publicity on MMR uptake^[18], and the Health Protection Agency attributed a large measles outbreak in 2008 and 2009 to the drop in MMR vaccination^[17].

Coverage later recovered, but not to the level needed to keep measles out. In 2025–26, 87.9% of children in England had a first MMR dose by 24 months, down from 91.6% in 2016–17, and 83.8% had both doses by age 5^[21]. The WHO target is 95%. In 2024 the UK recorded 3,681 measles cases, and WHO confirmed that endemic measles transmission had been re-established in the UK^[22].

Across the 53 countries of WHO’s European Region, 127,412 measles cases were reported in 2024 and 33,998 in 2025, and the number of countries with continuing or re-established endemic transmission rose from 12 to 19^[23]. By 7 November 2025 the Americas had 12,596 confirmed cases and 28 deaths that year, and Canada’s loss of elimination status meant the region lost it^[24]. The US reported 2,289 cases in 2025 and 3,471 in 2026 by 17 September, as MMR coverage among kindergarten children fell from 95.2% in 2019–20 to 92.4% in 2025–26^[25]. Worldwide, measles killed an estimated 95,000 people in 2024, mostly unvaccinated or under-vaccinated children under 5, while vaccination averted nearly 59 million measles deaths from 2000 to 2024^[26].

Falling coverage has many causes; in England, first-dose coverage at 24 months was 84.3% in the 30 most deprived local authority areas against 91.0% in the 30 least deprived^[21]. But the autism myth persists: a 2026 systematic review of 20 studies, mostly of caregivers of autistic children, found that hesitancy was consistently linked to “the disproven MMR-autism claim”, alongside safety concerns and distrust^[27].

The myth has also harmed autistic people and their families

In six US health systems, 81.6% of autistic children were fully vaccinated with the vaccines due at ages 4 to 6, compared with 94.1% of non-autistic children. Only 76.7% of younger siblings of autistic children had an MMR dose on time at age 1 to 2, against 93.5% of younger siblings of non-autistic children^[28]. In the 2026 review, caregivers of autistic children had 2.31 times the odds of vaccine hesitancy or refusal of caregivers of non-autistic children (95% CI 1.66 to 3.22)^[27]. The US researchers concluded that autistic children and their younger siblings “are at increased risk of vaccine-preventable diseases”^[28]. Autistic children deserve the same protection from measles as every other child.

There is a second harm. For almost three decades the scare has asked parents to weigh autism against measles, as though an autistic child were the worse outcome. The Autistic Self Advocacy Network, run by and for autistic people, said in 2015: “Vaccinations do not cause autism – but the use of autism as a means of scaring parents from safeguarding their children from life-threatening illness demonstrates the depths of prejudice and fear that still surrounds our disability.” Autistic Americans, it added, “deserve better than a political rhetoric that suggests that we would be better off dead than disabled”^[29]. In 2026 it wrote: “It is a big problem when people hear that autism is a tragedy. It makes people assume that autistic people’s lives must be bad because we are autistic”^[30]. In the UK, Mel Merritt, Head of Policy and Campaigns at the National Autistic Society, called the US administration’s September 2025 claims about vaccines and paracetamol “dangerous pseudo-science” that was “putting pregnant women and children at risk and devaluing autistic people”^[31].

Autism is not an injury, and autistic children are not damaged versions of the children their parents expected. What does shape autism is a separate question, covered in what research says about the causes of autism; why more people are diagnosed than a generation ago is covered in how many autistic people there are worldwide.

What the evidence asks of us

• Public bodies should speak from the evidence. WHO “advises all national authorities to rely on the latest science and ensure vaccine policies are grounded in the strongest available evidence”^[1].
• Research money should follow what autistic people need. In 2004 the Institute of Medicine did not consider “a significant investment in studies of the theoretical vaccine-autism connection to be useful at this time”^[14]. In 2025, autism organisations said that searching again for a link “detracts from the current wishes and needs of the autism community”, and called for research on “community needs, personalized health care, and services”^[16].
• Health services should meet worried families with patience, not blame. The 2026 review recommends “autism-informed counselling, explicit myth-correction by trusted clinicians, and service adaptations”^[27], including for autistic families, whose younger children are more likely to be missed.
• No one should be left behind. UKHSA says measles elimination depends on reaching the 95% target and “using all opportunities to catch up older children and adults who missed out when they were younger”^[22].
• Stop presenting autism as the thing to be feared. Correct the myth without treating autistic lives as a disaster. In ASAN’s words: “Let’s talk about what autistic people need, and about our rights”^[30].

For the wider picture, see our global evidence overview and the full Autism & Health research library.

Language: this piece uses identity-first language (“autistic people”), the preference of most autistic-led organisations, and uses clinical terms such as “autism spectrum disorder” only when naming a study or diagnostic category.

Why we're publishing this

Health Insurance UK is a commercial health-insurance resource, not a charity and not a campaign. We compiled this because autistic people, their families and the autistic-led organisations who have answered this myth for years deserve a clear, sourced summary to hand to a worried parent, a GP or a journalist. The case that autistic lives must not be used to frighten anyone belongs to the autistic community; our part is to set the research beside it and say plainly what it shows.

How to read this data

These studies are observational, comparing vaccinated with unvaccinated (or more with less exposed) children, because withholding vaccines at random would be unethical. They use different effect measures (relative risk, hazard ratio, odds ratio, rate ratio); for an outcome as uncommon as an autism diagnosis these are broadly comparable, and 1.0 means no difference. The largest evidence comes from Denmark and the US, with studies from the UK and Japan; Danish cohorts overlap, so their sizes should not be added. The retracted 1998 paper is cited only to describe its claims. Measles and coverage figures are official statistics for the dates shown and are not directly comparable between countries. Vaccination rates for autistic children and siblings come from US children born 1995 to 2014. This is analysis of published research, not new research.

Use this data

Free to cite with attribution to Health Insurance UK. Charities, campaigners and journalists are welcome to reuse these figures and charts. For the underlying figures as a spreadsheet, get in touch.

Important: This article summarises published research for general information. It is not medical advice and cannot be used to diagnose, treat or predict anything about an individual. If you have concerns about your own or someone else’s health, or about vaccination, please speak to a qualified health professional.

Sources

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