In recent days, the American Centers for Disease Control and Prevention (CDC) has updated the information available on the relationship between vaccines and autism, arousing great international attention for a new statement that is as significant as it is unexpected. According to the US Public Health Agency, a previously widespread statement taken as certain no longer fully reflects the state of current scientific knowledge.
Let’s try to better understand what the update says.
Vaccines and autism: what the CDC update says
On November 19, 2025, the CDC posted an update on its website stating:
The statement “Vaccines do not cause autism” is not a statement based on scientific evidence. Scientific studies have not ruled out the possibility that childhood vaccines contribute to the development of autism.
According to the agency, this statement does not imply the existence of clear evidence of a causal link, but it recognizes that the studies available so far do not allow it to completely exclude a possible role of vaccines.
The CDC also states that:
Although the cause of autism is likely to be multifactorial, the scientific basis to completely rule out a potential contributing factor has not yet been established. For example, one study found that aluminum-based adjuvants in vaccines had the highest statistical correlation with increased prevalence of autism among several suspected environmental causes. The correlation does not prove causation, but merits further study.
Meanwhile, HHS (Health and Human Services) has initiated a comprehensive evaluation of the causes of autism, which also includes the analysis of possible biological mechanisms between childhood vaccines and autism, the study of aluminum-based adjuvants present in many vaccines and the evaluation of any vulnerable subgroups, such as children with mitochondrial disorders or other genetic predispositions.
The CDC also points out that there are no studies yet that fully support the claim that any of the 20 doses of the seven childhood vaccines recommended in the US in the first year of life (DTaP, Hepatitis B, Hib, IPV, PCV, rotavirus, and influenza) cause autism.
Vaccines and historical studies
Over the years, several institutions have examined the possible link between vaccines and autism. Here’s what emerged from the major reviews:
1991 – Institute of Medicine
The first review did not identify data that addressed the question of a relationship between DPT (diphtheria, pertussis, tetanus) vaccination or its antipertussis component and autism. No experimental data were found indicating a possible biological mechanism.
2012 – Institute of Medicine
The review concluded that “the evidence is inadequate to accept or reject a causal relationship” between vaccine containing diphtheria toxoid, tetanus toxoid, or acellular pertussis and autism. The only study identified involving DTaP and autism found an association, but was discarded because it used data from a passive surveillance system and did not have an unvaccinated comparison population.
2014 – HHS Agency for Healthcare Research and Quality (AHRQ)
A comprehensive review concluded that there was insufficient evidence to accept or reject a causal relationship between DTaP and autism.
Regarding the hepatitis B vaccine, a cross-sectional study found a threefold risk of reporting autism among infants who received the vaccine in the first month of life compared to those who did not receive it. However, the AHRQ determined that there was insufficient evidence of an association.
2021 – AHRQ Update
Previous findings on insufficient evidence remained unchanged. No new studies were identified, and the scientific evidence continued to be considered insufficient to support or exclude a causal relationship.
MMR vaccine (measles, mumps, rubella)
The MMR vaccine has been studied most extensively. The IOM and AHRQ reviews argue, with high strength of evidence based on observational studies, that there is no association with autism spectrum disorders.
However, the CDC highlights some methodological limitations:
The CDC also points out that many studies (such as the 2002 New England Journal of Medicine study on the Danish population) may not be directly applicable to the US population, as vaccination schedules differ between countries.
Aluminum in vaccines
Then there is the aluminum issue to consider. Some preliminary studies have found a statistical correlation between exposure to aluminum-based adjuvants in vaccines and an increase in the prevalence of autism. The CDC clarifies in this regard:
The correlation does not prove causation, but merits further study.
According to the data cited, the 2019 CDC vaccination program resulted in a total vaccine-related exposure of 4,925 mg of aluminum by 18 months of age. A large Danish cohort study reported no increases in the risk of neurodevelopmental disorders, but a detailed analysis of supplementary tables showed a statistically significant 67% increase in the risk of Asperger’s syndrome for every 1 mg increase in aluminum exposure among children born between 2007 and 2018.
Future HHS research will therefore include analysis of high, low and zero exposures to aluminum, evaluating possible effects on chronic childhood diseases, including autism.
Because the statement “vaccines do not cause autism” is still visible on the CDC website
Despite the content update, the header of the CDC page still contains the wording “Vaccines do not cause autism”, but followed by an asterisk. The CDC explains:
The heading ‘Vaccines do not cause autism’ was not removed due to an agreement with the chairman of the US Senate Committee on Health, Education, Labor and Pensions that it would remain on the CDC website.
However, the content of the page has been modified to clarify that this statement “it is not a statement based on scientific evidence” and that studies have not ruled out the possibility that childhood vaccines contribute to the development of autism.
The agency specifies that the page will be further updated with scientific data resulting from the comprehensive HHS evaluation of the causes of autism.
