Unclear vaccine communication fuels doubt and hesitancy

The scientific consensus is that vaccinations are neither causally nor statistically linked to autism. The US health authority CDC changed its official communication on this matter and instead emphasized a connection could not be scientifically ruled out. An international research team from Vienna, Erfurt, Hamburg, and Copenhagen, led by the University of Vienna, has now investigated the consequences of this. The results are clear: those who read the current statement were less willing to get vaccinated. Furthermore, this led to decreased trust in the health authority and encouraged the endorsement of science denialist thinking. The societal consequences of such communication are therefore manifold; the researchers call for new guidelines to ensure careful and evidence-based communication by health authorities. The findings have recently been published in the renowned journal Science. 

Communication from health authorities can have a significant influence on public opinion. In November 2025, particular attention was drawn to the fact that the US Centers for Disease Control and Prevention (CDC), under pressure from the Trump administration, changed its official website communication on vaccinations and autism. In doing so, it highlighted alleged uncertainties regarding the current state of research and called for further investigations into the claimed link between vaccinations and autism. Previously, the scientific consensus had been clearly communicated that vaccinations are neither causally nor statistically linked to autism. An international research team from Vienna, Erfurt, Hamburg, and Copenhagen, led by psychologist Robert Böhm from the University of Vienna, investigated the consequences of this change in communication. 

Just under 3,000 US citizens took part in the study 

In a large-scale online study involving 2,989 adults in the US, the authors investigated how the changed communication strategy by the US health authority, the CDC, affects perceptions of vaccinations and intentions to get vaccinated. In an experiment, participants were assigned to different groups and given different versions of the CDC website to read. Some of the participants read the earlier version of the CDC statement, which clearly stated the scientific consensus: there is no link between vaccination and autism. Another group received the newly introduced version, which emphasises uncertainty regarding a possible link between vaccinations and autism. A third group received no such statement, acting as a control.

Doubts rise, intention to get vaccinated falls 

The results were clear: those who read the altered information considered side effects of vaccines to be more likely, had greater concerns about vaccine safety, and showed lower intentions to get vaccinated. "Our study shows that the way information is communicated can itself be a risk factor," says psychologist Alina Schneider from the University of Vienna, summarising the findings. "It is not a question of concealing scientific uncertainty as a matter of principle. What is crucial is that it is communicated in a way that is consistent with the actual evidence – particularly on topics where there is already broad scientific consensus," adds Cornelia Betsch from the University of Erfurt and the Bernhard Nocht Institute for Tropical Medicine in Hamburg.

A decline in intention to get vaccinated is not without consequences for public health. "Even a moderate but sustained decline in vaccination rates could lead to more preventable illnesses, a greater burden on the healthcare system and rising societal costs," says Lau Lilleholt from the University of Copenhagen.

The implications extend beyond the issue of vaccination 

However, such shifts in communication can have even broader societal consequences. The message also reduced the study participants' trust in the CDC. At the same time, support for typical strategies of science denial increased – that is, ways of thinking, such as selectively quoting studies, unrealistic demands for evidence, or conspiracy-like thinking. 

High relevance for health communication 

The conclusion is clear: changes in health communication are not mere formalities, but can have real effects on trust, attitudes, and behaviour. The authors therefore recommend that significant changes to health messages be documented transparently, carefully aligned with the evidence, and – where possible – tested in advance to see how they are understood by the public.

"When uncertainty is communicated, this should always be accompanied by a transparent contextualisation within the overall state of research and a clear recommendation for action," urges study lead Robert Böhm. However, according to the study authors, current communication primarily sows unwarranted doubt and undermines trust in health authorities.

Summary: 

• Psychologists led by the University of Vienna have investigated the consequences of communication that runs counter to the scientific consensus of the US Centers for Disease Control and Prevention (CDC) regarding vaccinations.
• 2,989 adults in the US took part in the large-scale online study. 
• The results were clear: those who read the current message considered side effects of vaccinations to be more likely, were less certain about vaccine safety and showed lower intentions to get vaccinated.
• Furthermore, this led to reduced trust in the CDC and encouraged the endorsement of science denialist thinking. 
• The researchers' appeal: health communication should be transparently documented, carefully grounded in evidence and, where possible, tested for public understanding.