Body and brain

Are viral infections linked to autism?

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Adjusted sibling comparisons found no clear statistical evidence linking flu during pregnancy to autism; a separate COVID study found no clear statistical evidence of an overall autism association after infection during pregnancy. Some diagnosed infections with symptoms caught before birth, including cytomegalovirus (CMV), are linked to later autism diagnoses. That does not show that viral infections generally cause autism.

Why people believe it

There are real findings, including the congenital-infection link. In one survey, 19.1% of parents of autistic children reported an accident, injury or illness. They said it affected their child's behaviour or development. The question did not ask whether a virus caused autism. The survey authors give one possible reason families may develop different explanations: uncertainty about autism's causes.

“An infection during pregnancy causes it”

The infection and its timing matter. Karolinska Institutet reports on a study of over 500,000 children. It compared brothers and sisters whose mother had an infection in one pregnancy but not the other. It found no evidence of a link between that infection and autism. It covered infections requiring specialist care, excluding COVID. Shared genes or family circumstances can create an apparent link. Comparing brothers and sisters helps investigate that. But measurement errors can also weaken the estimated links in these comparisons.

“But some viruses affect babies before birth”

TORCH is a group of viral and nonviral infections babies can catch before birth. The 2026 study found a link between diagnosed TORCH infections and autism. The link remained when the researchers compared brothers and sisters. CMV is short for cytomegalovirus, a common virus found in people of all ages. In the population analysis, CMV caught before birth was linked to autism. These infections caused symptoms and were diagnosed. The study could not assess outcomes among people whose infections caused no symptoms. In the population analysis, the autism association was stronger when intellectual disability was also present. The association was also present without intellectual disability. The authors judged the overall population contribution modest.

“Flu or fever explains the link”

The 2026 influenza study compared brothers and sisters in both South Korea and Japan. It also took other measured factors into account. These comparisons found no clear statistical evidence linking flu during pregnancy to autism. A review of ten studies of neurodevelopmental disorders found a modest association between fever during pregnancy and autism in its autism subgroup analysis. Its authors warn that fever and infection are hard to separate. Another team suggested a mother's immune response might explain an influenza link, if that link is real.

“What about COVID during pregnancy?”

A 2026 study of SARS-CoV-2 infection during pregnancy followed 69,987 children. It followed them to ages 27–48 months. It found no clear statistical evidence of an overall autism association. A higher estimate in girls did not establish a difference between girls and boys. Family factors that were not measured and pandemic stress could affect the findings.

A separate review looked at SARS-CoV-2 exposure during pregnancy and early neurodevelopmental outcomes. It found no statistically significant overall link. Statistical significance depends on how likely these results, or stronger ones, would be if there were no real link. But the children were only 1–38 months old. First-trimester exposure was associated with poorer neurodevelopmental scores than exposure in the second or third trimester. This was based on just three studies with widely differing results.

“My child was ill before the diagnosis”

The childhood-infection study counted any infections needing specialist care. The researchers compared brothers and sisters, taking other measured factors into account and excluding congenital causes. They found a weak link with later autism without intellectual disability. The authors suggest being more prone to severe infections as one possible explanation. They also suggest early childhood infections may contribute to the risk of a later intellectual-disability diagnosis, including alongside autism. Other factors that were not measured could still explain associations.

“Behaviour changes during fever must be a clue”

Prospective parent surveys found consistent behavioural improvements during fever in only three of 141 autistic children. Symptoms generally worsened in both autistic children and typically developing controls. Behaviour worsened more in the autistic group. These children already had autism, so this cannot establish its original cause.

Official positions, with dates

WHO, 17 September 2025: evidence suggests genetic and environmental factors influence early brain development. Autism is not an infection. It cannot spread between people. CDC, 13 April 2026: scientists believe multiple causes act together.

What people also ask

Which four viruses have been linked to autism?

These studies do not establish a fixed list of four linked viruses. They separate infections acquired before birth from influenza and COVID during pregnancy.

What viral infections are linked to autism?

CMV acquired before birth was associated with autism in the population analysis. That result concerns diagnosed infections with symptoms, acquired before birth.

Are there more cases of autism since COVID?

CDC reported that higher autism identification in the younger birth cohort reappeared by the end of 2020. This followed disruption at the start of the pandemic. Its comparison involved children born in 2014 and 2018. So it cannot test COVID exposure before birth.

Is there a link between influenza and autism?

The 2026 influenza study compared brothers and sisters. It took other measured factors into account. It found no clear statistical evidence linking flu during pregnancy to autism in the children. That does not prove every possible effect is absent.

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