Uncertainty-based framing raises doubt, lowers vaccination intentions, and boosts science denial
Robert Böhm, Alina Schneider, Cornelia Betsch, and Lau Lilleholt
Science 30 Apr 2026 Vol 392, Issue 6797 pp. 475-477

The US Centers for Disease Control and Prevention (CDC) revised its public statement on vaccines and autism in November 2025, suggesting that a possible association between vaccination and autism has not been ruled out with sufficient scientific rigor. Despite its potentially far-reaching public health implications, little is known about how this policy shift, from the previous consensus-based message grounded in the prevailing evidence to the updated uncertainty-based message, affects public perceptions, attitudes, and vaccination intentions. Beyond vaccine-related outcomes, a shift toward uncertainty-based communication may shape broader societal responses, including political polarization around vaccine safety (1), erosion of institutional trust, and increased susceptibility to science-denial reasoning (2)—particularly when uncertainty is emphasized in areas where expert consensus is established. A large-scale online experiment tested the effects of the CDC’s shift in communication, showing that the new uncertainty-based statement amplifies public uncertainty, reduces vaccination intentions, and increases endorsement of science denial strategies.

Public debate over a purported link between vaccination and autism spectrum disorder has persisted for decades, despite a broad scientific consensus that vaccines are neither causally nor correlationally associated with autism (3). Misinformation on this issue remains widespread and consequential for public trust and health behavior (4). The CDC’s shift in communication can be understood as an administrative downstream consequence of recent policy and agenda changes that elevated autism as a federal priority (5), established a government-wide framework for how agencies should communicate scientific evidence—including how scientific uncertainties are framed (6)—and enabled more direct top-down political steering of CDC messaging. Although uncertainty is inherent to scientific inference, evidence-based communication must calibrate it to the strength of the available evidence and present it in the context of expert consensus, rather than implying uncertainty where there is overwhelming scientific agreement (7). By departing from the prevailing evidence base, this shift has reignited the debate over vaccine safety and the role of public health institutions in science-based communication—within an already polarized information environment where institutional signals are often interpreted through partisan lenses, rendering health decisions identity issues (1).

Scientific Evidence and Communication

The alleged vaccine–autism link originated with a study that reported an association between the measles–mumps–rubella vaccine and symptoms of autism spectrum disorder in children, but was later found to be methodologically flawed and ethically compromised, and eventually retracted (8). Despite this, concerns about a possible vaccine–autism link persisted as a recurring trope in narratives driving vaccine hesitancy and refusal and were extended to other vaccine components, including thimerosal—a mercury-based preservative—prompting scrutiny of other vaccines. Concerns over the claimed link have also encompassed aluminum-containing adjuvants and claims that an expanded vaccination schedule might overwhelm the developing immune system. Contrary to these claims, extensive research using a wide range of methodological approaches and drawing on data from millions of individuals across multiple countries has found no evidence of a statistical association between vaccines and autism (3). Notwithstanding this overwhelming body of evidence, claims linking vaccines to autism continue to circulate widely, highlighting the persistence of health-related misinformation and the challenges of effective science communication (4).

Under the leadership of the current US Secretary of Health and Human Services, Robert F. Kennedy Jr., the CDC substantially altered its vaccination communication strategy, culminating in an updated public- facing webpage addressing vaccines and autism. Since 19 November 2025, this webpage has asserted that “[t]he 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” and that “[s] tudies supporting a link have been ignored by health authorities.” The revised CDC statement stands in direct contrast to the agency’s earlier evidence-based guidance, which concluded “that there is no link between receiving vaccines and developing autism spectrum disorder ”—consistent with the scientific consensus and positions of other major health organizations, including the World Health Organization (3).

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