MMR vaccination and autism risk: population study results
Large investigations have found no association between MMR vaccination and increased autism risk. The combined vaccine protects against measles, mumps, and rubella. Research has examined broad child populations as well as children with an autistic older sibling, who already have a higher likelihood of an autism diagnosis. Those investigations have used national registries, insurance records, and systematic reviews. The finding of no increased autism risk is specific to that outcome; vaccine research separately measures effectiveness against infection and possible adverse effects such as febrile seizures.
In Denmark, researchers at Statens Serum Institut studied 657,461 children born between 1999 and 2010, following them from age 1 through August 2013. They linked data from the Danish Civil Registration System with data from the Danish Vaccination Registry and reports of autism diagnoses. The comparison included 31,619 children who had not received MMR. Autism occurred at similar rates among vaccinated and unvaccinated children. Among the children followed, 6,517 received an autism diagnosis during the study period. The work was published in Annals of Internal Medicine in 2019.
The Danish team also examined potentially susceptible groups. These included children with autistic siblings and groups defined by parental age, pregnancy complications, maternal smoking, and low birth weight. They investigated whether diagnoses clustered in particular periods after vaccination. No increased autism risk appeared in the vaccinated groups. An earlier Danish study published in 2002 had followed 537,303 children and likewise found no association.
A U.S. investigation published in JAMA in 2015 examined 95,727 privately insured children with older siblings. The researchers used administrative health claims and followed children enrolled from birth through at least age 5. Among the children studied, 994 received an autism spectrum diagnosis, and 1,929 had an older sibling with autism. Diagnoses were more common among children with an affected sibling. That underlying difference made the sibling groups useful for examining whether MMR was associated with additional risk among children already more likely to receive an autism diagnosis.
MMR receipt was not associated with increased autism risk in either sibling group. Vaccination rates were lower among children whose older sibling had autism: at age 2, 73% had received at least one dose, compared with 84% among children without an affected older sibling. By age 5, those figures were 86% and 92%. The analysis compared vaccination status at different ages and accounted for measured differences between children. Its population consisted of privately insured families, a feature that limits how directly every detail can be generalized to all children.
The Cochrane assessment of MMR-related vaccines examined a wider range of outcomes. Its 2020 update included 138 studies and more than 23 million children. Some studies measured protection against infection, while others investigated possible harms. The autism analysis involved two studies with 1,194,764 children and found no increased risk. The evidence for that outcome was rated moderate in certainty. The review also found small risks of febrile seizures and a clotting condition called idiopathic thrombocytopenic purpura, distinguishing those measured risks from the unsupported autism association.
Vaccine effectiveness was another part of the same assessment. For measles, the estimated effectiveness was 95% after one dose and 96% after two doses in the included cohort studies. For mumps, estimated effectiveness rose from 72% after one dose to 86% after two doses. The review distinguished MMR from formulations or schedules that include varicella, the virus causing chickenpox. The review included 51 effectiveness studies involving about 10 million children and 87 studies of unwanted effects involving about 13 million. Seventy-four studies had been added since the previous review in 2012.
In November 2025, the World Health Organization's Global Advisory Committee on Vaccine Safety assessed updated reviews of vaccines and autism. One review included 31 primary studies published from 2010 through August 2025, plus five meta-analyses. It examined thiomersal-containing vaccines and vaccines more broadly. The most rigorous studies and all five meta-analyses found no evidence supporting an association. Studies suggesting an association had substantial methodological problems and high risk of bias. The committee reaffirmed its earlier conclusion that vaccines do not cause autism.
A second WHO review examined aluminum-adjuvanted vaccines, including ten randomized controlled trials and seven large cohort studies. High-quality evidence did not support an association with chronic or systemic disease. Ecological studies suggesting an autism association could not establish individual causation and had serious methodological limitations. The committee also considered a newer Danish registry investigation covering children born between 1997 and 2018. Its conclusion remained unchanged. Across different populations, research designs, and proposed ingredients, the higher-quality evidence has consistently failed to support a causal vaccine-autism link.
- Statens Serum Institut, No Association between MMR Vaccine and Autism — en.ssi.dk
- Jain and colleagues, Autism Occurrence by MMR Vaccine Status, JAMA (2015) (archived copy) — web.archive.org
- Cochrane, MMRV vaccine effectiveness and harmful effects — www.cochrane.org
- WHO, GACVS statement on vaccines and autism (2025) — www.who.int