select search filters
briefings
roundups & rapid reactions
Fiona fox's blog
Scientists respond to reports of comments made by President Trump about vaccines, MMR and autism when speaking about an Executive Order.
Dr Monique Botha, Associate Professor in Social and Developmental Psychology, Durham University, said:
“The scientific evidence on MMR vaccination and autism is exceptionally extensive and consistent. There is no credible evidence that MMR vaccination causes autism. A 2014 meta-analysis1 included five cohort studies involving 1,256,407 children, alongside five case-control studies involving a further 9,920 children, and found no association between vaccination and autism or autism spectrum disorder. A subsequent nationwide Danish cohort study2 followed 657,461 children and again found that MMR vaccination did not increase autism prevalence, including among children considered more susceptible because of factors such as having an autistic sibling. The question has therefore not been neglected or insufficiently investigated. It has been examined repeatedly, in very large populations, using different study designs and in different countries, with remarkably consistent results.
“It is important not to mistake two things increasing over historical time for evidence that one caused the other. Recorded autism prevalence has risen substantially, but the way autism is defined, recognised and diagnosed has also changed enormously3 and this is important to keep in mind. Diagnostic criteria have broadened, gender disparities and racial disparities are decreasing, awareness has increased, children are identified earlier, and many people who would previously have received another diagnosis, or no diagnosis at all, are now recognised as autistic and rightly so. The fact that vaccination programmes also expanded over parts of the same historical period cannot establish causation. The relevant scientific question is whether autism prevalence is higher among vaccinated children than among comparable unvaccinated children, and the large epidemiological literature directly examining that question does not support a causal relationship in any capacity.
“From an autism research perspective, claims that children are receiving “too many vaccines” are also concerning because they revive an outdated idea that autism represents some form of vaccine-induced neurological injury or immune overload. Autism is a neurodevelopmental phenomenon4 with primarily genetic contribution and complex developmental origins. It is not scientifically justified to suggest routine childhood vaccination is a cause of autism simply because autistic characteristics often become apparent during the same period of childhood in which vaccinations are administered.
“The same principle applies5 to claims about the overall number of vaccines children receive. Increasing overall exposure to anti-body stimulating proteins found in vaccines is not associated with a higher odds of autism. The fact that contemporary children are protected against more diseases than children were several decades ago is not, by itself, evidence that modern vaccination schedules increase autism prevalence.
“Questions about vaccine ingredients should also be treated as scientific questions rather than rhetorical devices. Aluminium salts have been used as adjuvants in some vaccines for decades. It is entirely appropriate for vaccine safety to remain under ongoing surveillance, but the available evidence does not support claims that the small quantities of aluminium used in vaccines increase autism prevalence.
“There is also an important opportunity cost when political and scientific attention is repeatedly redirected towards a causal hypothesis that has already been investigated at enormous scale. Autistic children, autistic adults and their families have real and pressing needs that deserve scientific, clinical and political attention. We should be investing in early and timely access to diagnosis, appropriate support, inclusive education, equitable healthcare, employment, community participation and the conditions that enable autistic people to live healthy, fulfilling and self-determined lives. We should also be addressing the substantial health inequalities experienced by autistic people across the lifespan, and ensuring that families can access meaningful support when they need it.
“Continuing to debate the long-discredited claim that vaccines cause autism does nothing to meet those needs. It consumes finite research funding, scientific expertise, clinical capacity and public attention that could instead be directed towards questions capable of materially improving autistic people’s lives. Autistic people do not need another generation of research devoted to asking whether vaccines caused autism. They need research, services and policy focused on enabling them to live healthy, equitable and fulfilling lives. Repeatedly diverting scarce research resources back towards a causal hypothesis that has already been tested across millions of children represents a genuine opportunity cost for autism research.
“There is then a broader concern about political interference in established science. Scientific evidence should inform political decision-making, but political preference should not be allowed to manufacture scientific uncertainty where a substantial and consistent evidence base already exists. Governments are entitled to make policy choices and to commission further research, but reopening a repeatedly tested causal claim without compelling new evidence is not the same thing as discovering that the scientific evidence has changed.
“This distinction matters because legitimate scientific scrutiny depends on evidence. Science must always remain open to revision, and no conclusion should be protected from challenge simply because it is longstanding, however, challenging an established conclusion requires evidence capable of challenging it. Political actors repeatedly presenting a well-tested question as though scientists simply have not looked hard enough risks shifting the boundary between legitimate scientific debate and political meddling in science.”
1 https://pubmed.ncbi.nlm.nih.gov/24814559/
2 https://pubmed.ncbi.nlm.nih.gov/30831578/
3 https://www.bmj.com/content/392/bmj-2025-084164
4 https://jamanetwork.com/journals/jamapsychiatry/fullarticle/2737582
5 https://www.jpeds.com/article/s0022-3476(13)00144-3/fulltext
Dr Amanda Roestorf, Director of Research, Autistica, said:
“One of the most persistent myths is that vaccines, particularly the MMR vaccine, cause autism. This claim has been extensively studied over several decades, by world-leading scientists, and is not supported by the scientific evidence. The World Health Organization and numerous large, high-quality studies have consistently found no link between vaccines and autism.
“Misinformation about autism and vaccines is harmful, misleading and distracts from the real support autistic people need.
“Vaccines recommended in childhood undergo extensive testing before approval and are continuously monitored for safety. Public health recommendations are based on careful evaluation of the benefits and risks of vaccination, with the aim of protecting children and communities from serious infectious diseases.
“Claims that the MMR vaccine is ‘lethal’ or that it causes autism are not supported by evidence. In contrast, measles, mumps, and rubella can all cause serious illness, long-term complications and, in some cases, death. Vaccination remains one of the safest and most effective ways of preventing these diseases.
“Current evidence also shows that administering recommended vaccines according to established schedules is both safe and effective. Decisions about vaccine schedules should be guided by robust scientific evidence and expert clinical advice.
“The evidence is clear: vaccines do not cause autism. Efforts to support autistic people should focus on improving access to timely assessment, appropriate support and high-quality care. Autistic people and their families deserve accurate information grounded in evidence. Autistic people deserve facts, not fear.”
Dr David Elliman, Honorary Associate Professor and paediatrician, UCL, said:
“This announcement comes as a surprise, not because the President’s views were unknown, but because it was felt he wouldn’t try to turn such outlandish unscientific views into policy without at least a semblance of evidence. He has proffered no new evidence.
“The previous change to the US schedule, which reduced the number of recommended vaccines, was supposedly modelled on ‘peer countries’ in Europe. This was false and has been repeatedly exposed as such.
“The new move to split up combination vaccines, including MMR, and give only one vaccine at each visit, is not based on any scientific evidence. No country in the world recommends splitting the MMR into its 3 components and no country in the world recommends giving only one vaccine at each visit. There are bucket loads of evidence supporting current policies and none supporting the proposed changes.
“Does it matter? Yes, it matters enormously for many reasons.
“There is not enough of the components of the MMR vaccine available in a form to be given as single vaccines yet. Will some people in the US now hold off vaccinating against measles etc. until the separate vaccines become available? The US already has the largest numbers of cases of measles for decades. If a significant number of people do delay vaccination for whatever reason, there will likely be avoidable suffering and death.
“Even when vaccines do become available, we know from vast experience that the more complex a programme is, with increasing numbers of visits, the less likely that all vaccines will be given. Already suboptimal vaccine uptake will fall.
“The overwhelming majority of the medical profession do not believe there is a link between MMR, or any vaccine, and autism. Already, in the US, professional bodies are having to produce recommended vaccination schedules different from those of the government. Their recommendations are made on the basis of the scientific evidence and the best interests of their patients. These different recommendations will confuse patients and put their doctors in a very ethical difficult position. Should they do what is best for their patients or follow the scientifically unfounded comments of the President? Reassuringly, it looks like they will follow their professional ethical principles.
“Individual states within US make local policy and already a political divide is appearing. What a tragedy it would be if your chances of catching measles and running the risk of dying depended on what political party your place of residence supported!
“Most professional and government bodies outside the US now no longer hold US statutory health bodies in the esteem that they used to. I do not see other countries moving to change their policies, however, it would be naive to think that populations will not be affected. At the very least, some people will likely look upon this as casting doubt on vaccine safety and may withhold or delay some vaccines.
“We know from past experience with unfounded vaccine scares that it is relatively easy to destroy confidence, but takes a long time to restore it. It is important that all healthcare professionals and researchers stand up for the welfare of children and call out anything likely to be detrimental. Politicians have an obligation to ensure that they also follow this principle, rather than propagate unfounded dangerous whims.”
Prof Angelica Ronald, Professor of Psychology and Genetics, University of Surrey, said:
What do we know from scientific evidence about any link between MMR and autism?
“Autism is caused by a combination of genetic and environmental influences. Genetic differences are the biggest explanation for the causes of autism. These genetic differences include both the common genetic differences that many of us have in our DNA as well as some rare types of genetic differences that only a few people have.
“The environment plays a smaller role in influencing which children develop autism. Birth complications are likely to play a role for some children in combination with their genetic factors. We know this from twin studies comparing identical and fraternal twins, which examined both birth complications and autism.
“Large population studies of millions of children show that autism is not linked to MMR. Further evidence comes from studies in countries in which the MMR vaccine was halted such as Japan. In Japan, when the MMR vaccine was stopped, autism cases still continued to rise. Furthermore, genetic factors are the largest known cause of autism and this is supported by many robust, well-powered studies. Finally, some traits related to autism emerge before children receive the MMR vaccine. In sum, at least four forms of independent evidence do not support any link between autism and MMR.
What do we know from scientific evidence about autism rates now versus when there were fewer vaccines – and does this mean the two things are linked?
“Autism rates and vaccine use have both risen over similar time periods in some countries but this does not prove or even suggest that vaccines cause autism. This is because correlation does not prove causation; many things rise together over time without one causing the other.
“Rates of autism used to be lower and this could be for many reasons. One reason is less awareness of autism in previous years. A second reason is that autism is now defined more broadly. There are likely to be multiple reasons for the increase in autism cases and this is being investigated by researchers. A third reason is growing awareness that obtaining a diagnosis will help autistic people to find appropriate support in schools or their workplace. There is not strong evidence for the hypothesis that autism is increasing due to increased use of vaccines.
“There are many sources of scientific evidence to show that the increase in autism rates is not caused by the increased use of vaccines. Large population studies of millions of children show that autism is not linked to vaccine use. Further evidence comes from countries where vaccine use was paused, such as Japan, where MMR use was halted. In Japan, when the MMR vaccine was stopped, autism cases still continued to rise. Furthermore, genetic factors are the largest known cause of autism. Finally, some traits related to autism emerge before children receive most vaccines. In sum, at least four forms of independent evidence do not support a link between autism and vaccines.”
Prof David Salisbury FMedSci, Associate Fellow, Programme for Global Health, Royal Institute of International Affairs, Chatham House, said:
“There is not a shred of evidence that the provision of single vaccines would prevent autism. There is a wealth of evidence that has failed to find a link between vaccines, especially MMR, and autism. When Wakefield demanded the provision of single vaccines in the UK in the late 1990s and early 2000s, the manufacturers made clear that they would not provide them, not least because they were no longer licensed. Twenty five years later, the situation in the US is the same. Single vaccines are not licensed. It is unfortunate that nobody appears to have told Trump.”
Prof Azeem Majeed FMedSci, Professor of Primary Care and Public Health, Imperial College London, said:
“The MMR vaccine has an extensive safety record. Large-scale studies, including multiple nationwide cohort studies, have consistently shown it is highly effective at preventing measles, mumps and rubella with only generally mild side effects such as transient fever. There is no credible scientific evidence that the combined MMR vaccine has a meaningful risk of severe or fatal outcomes in healthy children.
“Extensive high-quality evidence, including large cohort studies from Denmark and elsewhere, meta-analyses, and systematic reviews by bodies such as the Cochrane Collaboration and the Global Advisory Committee on Vaccine Safety, have found no causal link between the MMR vaccine (or vaccines in general) and autism spectrum disorder. The childhood immunisation schedule recommended by bodies such as the American Academy of Pediatrics is based in decades of data on disease epidemiology, vaccine efficacy, safety, and the practical benefits of timely protection against diseases that can still cause significant morbidity and mortality. Reducing the number of universally recommended vaccines risks leaving children unprotected against diseases for which the benefits of immunisation clearly outweigh the risks.
“Administering multiple vaccines at the same visit has been extensively studied and is both safe and advantageous: it reduces the number of healthcare encounters, improves completion rates, minimises periods of vulnerability to infection, and does not overload the immune system. Spacing vaccines across many separate visits increases the likelihood of delayed or missed doses and leaves children susceptible for longer, with no demonstrated safety benefit in healthy children.
“Aluminium salts have been used as adjuvants in certain vaccines for many years to enhance immune responses. The quantities involved are very small (far below established safety thresholds) and large epidemiological studies have found no association with autism, autoimmune disease, asthma, or other chronic conditions.
“In summary, the scientific consensus, based on extensive observational and experimental evidence, supports the safety and public-health value of the established childhood immunisation programme, including the combined MMR vaccine. Claims linking these vaccines to autism or describing the combination product as dangerous are not supported by the evidence.”
Prof Adam Finn, Emeritus Professor of Paediatrics, University of Bristol, said:
“It is critical that information about the importance, effectiveness and safety of the vaccines we offer parents to be given to their children is evidence-based and accurate. The combined measles mumps rubella vaccine has been widely used in the UK since the 1980s as well as most other European countries and its safety has been extensively researched and reconfirmed. Dividing the vaccine into separate components makes no logical sense and is infeasible at this time in any case as no such vaccines are available. The evidence concerning all the vaccines routinely offered for children on the NHS is constantly reviewed and updated. Parents can be confident that our health system offers vaccines that are effective, safe and that children genuinely need in order to be protected from the threat of serious infectious diseases.”
Dr Ruth Griffin, Associate Professor of Vaccinology, University of Nottingham, said:
What do we know from scientific evidence about the safety of the MMR vaccine?
“Since the MMR vaccine was introduced over five decades ago, investigations of its safety are now extensive. This vaccine contains the live attenuated form of all three viruses. As with other vaccines, there is a trade-off between immunogenicity and tolerability and no vaccines have zero risks. However, the known risks associated with MMR are uncommon and generally much smaller than the risks of infections themselves and there is an accumulation of strong evidence that MMR is not associated with autism.
“Following the 1998 publication of Andrew Wakefield’s now-discredited claim linking MMR with autism, MMR uptake fell substantially. Measles subsequently returned in larger numbers, including major outbreaks in the 2000s. Measles is extremely contagious. According to WHO guidance, at least 95% coverage with two measles vaccine doses is required to stop transmission and protect communities from outbreaks.
“Global immunization efforts have led to an 88% drop in measles deaths between 2000 and 2024, according to the World Health Organization (WHO). Nearly 59 million lives have been saved by the measles vaccine since 2000.
“However, an estimated 95 000 people, mostly children younger than 5 years of age, died due to measles in 2024. While this is among the lowest annual tolls recorded since 2000, every death from a disease that could be prevented with a highly effective and low-cost vaccine is unacceptable.
“Despite fewer deaths, measles cases are surging worldwide, with an estimated 11 million infections in 2024 – nearly 800 000 more than pre-pandemic levels in 2019.”
Prof Helen Bedford, Professor of Child Public Health, UCL Institute of Child Health, UCL, said:
“MMR vaccine has been used in the USA for over 50 years since the early 1970s and in the UK since 1988. It is highly effective and has an excellent safety profile. Like all vaccines, it can give rise to mild side effects such a fever, feeling off colour and as it is a live vaccine, symptoms of mild measles, mumps and rubella; these are innocuous, short lasting and not infectious. Occasionally side effects are more severe such a fits. The side effects of vaccines need to be balanced against the impact and complications of the diseases they prevent. Measles, mumps and rubella all have serious effects. We have already seen child deaths from measles this year in UK. A large body of research conducted over the past two decades has found strong evidence of no link between MMR vaccine and autism. The vaccine has, and continues to save, millions of lives. The three vaccines have never been administered as separate doses to young children as part of vaccination policy so that policy’s safety and effectiveness are unproven. However, just by delaying protection it would be a serious step backwards for protecting our children’s health.”
Dr Ben Kasstan-Dabush, Assistant Professor in Global Health & Development, London School of Hygiene & Tropical Medicine, said:
“The Measles, Mumps, Rubella (MMR) vaccination has a proven track record of being highly safe, effective and well tolerated, and Wakefield’s claim of a link to autism robustly rejected as a fabrication. Measles-containing vaccination, in particular, is credited with having the greatest contribution to reducing child deaths, sickness, and disability of any vaccination over the past 50 years.
“There is no evidence that offering the MMR vaccination as single injections is a safer or more effective method of immunising children. To the best of my knowledge there is no country that offers single injections as part of their national vaccination schedules, making the decision taken in the US to recommend splitting the MMR vaccination an experiment rather than an evidence-based decision.
“This move will further obstruct efforts to contain measles outbreaks that have persisted in the US, where there have been 2,465 confirmed measles cases reported as of 6 August 2026 and three deaths linked to measles in 2025. The Trump administration have a responsibility to explain how their latest recommendations will help to contain these outbreaks and the consequences for families. There is a very real risk that single injections will lead to decreased vaccination uptake, and would put more children at risk of vaccine preventable-diseases.
“UK families should be reassured that recommendations made by the Joint Committee for Vaccines and Immunisation are firmly rooted in evidence. The NHS vaccination schedule recommends that children receive two MMR/MMRV doses, administered alongside other vaccinations. At no point in the schedule is a child called in to a GP surgery to receive only one vaccination. Single injections would involve parents bringing their children for at least 6 separate appointments (or 8 in the case of MMRV). This would increase the risk of exposure to vaccine-preventable diseases, because children would need additional time to be brought up to schedule, and the burden on primary care teams as they need to offer more appointments per child.
“Offering single vaccinations may also influence parental risk perceptions, and lead parents to getting one vaccine (e.g. measles) for their child but not another (e.g. rubella). This scenario would be dangerous because children would not complete the full course of MMR vaccination so that they would not be protected, while also eroding population immunity and increasing the risks to those who cannot be vaccinated.”
Prof Sir Andrew Pollard, Director of the Oxford Vaccine Group and Ashall Professor of Infection and Immunity, Pandemic Sciences Institute and Department of Paediatrics, University of Oxford, said:
“The US administration’s decision to reduce the number of vaccines recommended for children, deprioritising jabs with a proven track record of effectiveness against serious diseases, and questioning the proven safety of vaccines in the process, undermines public confidence in the cornerstone of child health in the country. Vaccine programmes have been built by scientific evidence over decades and introduction of vaccines that make up a programme takes account of a country’s disease risk, health system and population demographics to make the best decisions to minimise serious illness and death in the population, and to assess affordability for the health system. These interventions are extensively tested and monitored, which is why we know that vaccines do not cause autism. The US immunisation programme saved an astonishing 1.1million lives in the country in the past 30 years (1994-2023), according to US Centers for Disease Control estimates. Changes in vaccination programmes can be appropriate when disease risk changes or new evidence emerges, but such changes should be driven by scientific evidence developed by individuals with the necessary expertise and not by whim, because the lives of children are at stake.”
Prof Michael Absoud, Professor of Paediatric Neurodevelopmental Disability, Faculty of Life Sciences & Medicine, King’s College London, said:
“The scientific evidence does not support a causal link between the MMR vaccine and autism.
“Large population studies and systematic reviews involving millions of children have found no increased risk of autism after MMR vaccination.
“One reason the MMR vaccine has been wrongly suspected is that the first dose is given at around the same age when early autistic differences, including slowing or loss of skills in some children, may first become apparent to parents.
“Temporal association is not the same as causation, and the fact that autistic features may become more noticeable in the second year of life does not mean that a vaccine given around that time caused autism.
“The original 1998 Lancet paper that suggested a link between MMR, bowel symptoms and autism was based on a very small and highly selected sample, was later retracted, and has been found to have involved serious scientific and ethical failings.
“The subsequent evidence has moved strongly in the opposite direction: carefully conducted epidemiological studies have not found that MMR causes autism.
“Autism diagnoses are more common now than decades ago, but this does not mean vaccines are the cause.
“The increase in autism diagnosis is best understood as reflecting multiple factors, including broader diagnostic criteria, greater awareness, improved recognition in children previously missed, and changes in clinical and educational practice.
“Autism is a highly heterogeneous neurodevelopmental condition with strong genetic contributions and smaller complex prenatal and perinatal influences; it is absolutely not explained by a single postnatal exposure such as MMR.
“Like all medicines, vaccines can have side effects, but serious adverse reactions to MMR are very rare, and the risks of measles, mumps and rubella themselves are substantially greater.
“Measles is not a trivial childhood illness: it is highly infectious and can cause pneumonia, encephalitis, long-term disability and death.
“Splitting MMR into separate measles, mumps and rubella vaccines is not supported by evidence as safer or better.
“Separating vaccines can leave children unprotected for longer and increases the risk that some children will not complete the full course.”
Declared interests
Dr Monique Botha: “I have received research funding from the Leverhulme trust, the ESRC, UKRI, Royal society of Edinburgh, for other research not related to this topic but never from a pharmaceutical company, nor have I done any work for pharmaceutical companies. My work has never been sponsored by a company and they have never paid for me to attend conferences or other events. I have no conflicts of interest whilst talking about vaccines and their evidence in regards to autism.”
Dr Amanda Roestorf: “I have no declarations of interest to report.”
Dr David Elliman: “I have no conflicts of interest.”
Prof Angelica Ronald: “Receive research funding from Simons Foundation Autism Research Initiative, Waterloo Foundation and UK Genetics Society.
Act as joint editor of Journal of Child Psychology and Psychiatry, for which I receive an annual honorarium from Association for Child and Adolescent Mental Health.
Funded by the International Society for Autism Research to give their autism research keynote speech at this year’s conference.
Executive committee member of the Behaviour Genetics Association 2025-26.”
Prof David Salisbury: “No interest relevant to MMR vaccine.”
Prof Azeem Majeed: “I don’t have any conflict of interest.”
Prof Adam Finn: “AF was formerly a member of the UK national technical advisory group the JCVI and chair of the WHO Euro Technical Advisory Group of Experts on Immunisation. He now works as a paid consultant to all the major manufacturers of childhood vaccines as well as several startup companies with candidate vaccines undergoing development studies and clinical trials.”
Dr Ruth Griffin: “No conflicts of interest.”
Prof Helen Bedford: “No conflicts.”
Dr Ben Kasstan-Dabush: “No conflict of interest to declare.”
Prof Sir Andrew Pollard: “Director of the Oxford vaccine group and former chair of JCVI.”
Prof Michael Absoud: “No conflicts.”