Vaccines have long been considered by experts to be among the most studied medical interventions, and on the whole, Americans are still broadly supportive of them. But during President Donald Trump’s second term, the agency that makes recommendations about vaccines—the U.S. Centers for Disease Control and Prevention (CDC)—has, without new scientific evidence, cast fresh doubt on their safety and resurfaced the disproven link between vaccines and autism.

Before Nov. 19, 2025, the CDC’s website was unequivocal on the topic: “Studies have shown that there is no link between receiving vaccines and developing autism spectrum disorder,” it read. After Nov. 19, the guidance essentially reversed. “The 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,” it now says. “Studies supporting a link have been ignored by health authorities.”

That claim, reflecting the longstanding vaccine-skeptical views of Robert F. Kennedy Jr., Secretary of Health and Human Services (HHS), is false. But new research published in the journal Science suggests that it’s affecting what Americans believe about vaccines.

“What concerns me is not only the immediate effect on vaccine attitudes, but also the broader downstream effects: reduced trust in the CDC and greater endorsement of science-denial practices may shape how people will engage, or not engage, with information about vaccines more generally,” says Robert Böhm, professor of psychology at the University of Vienna, who led the new study.

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To conduct their work, Böhm and his colleagues asked nearly 3,000 U.S. adults a range of questions about the safety and efficacy of vaccines. They also asked who should be trusted for information on vaccines and what standard of proof the medical community should demand in determining risks associated with vaccination.

Before answering the questions, people read the CDC’s former position on vaccines and autism, the CDC’s new stance, or nothing at all.

Reading the statements seemed to influence how people felt about vaccines. The group that read the CDC’s old position, for example, was less likely to believe that vaccines might cause adverse effects; the group that read the new, more skeptical position was a bit likelier to believe it. When people were asked if they would get a recommended vaccine, those who read the new position were less enthusiastic than those who read the old one. Trust in the CDC itself was boosted by the old vaccine statement and lowered by the new one.

The researchers also looked at some of the tropes and arguments the anti-vaccine movement often deploys and measured how people’s belief in them was affected by reading the two statements. A favorite device used by vaccine skeptics is to set impossible standards of scientific proof and defy the pro-vaccine side to meet them. People in the study were therefore asked to evaluate the claim that “health authorities should only say that vaccines do not cause autism once every possible link has been ruled out for every child, with complete certainty.” Cherry-picking is another tactic vaccine skeptics often use. “If I can find at least one scientific study that suggests vaccines might be harmful,” the study posited to people, “that is enough reason to doubt the many studies that find no serious risk.”

Logical fallacies were tested too, with the statement, “If some children develop autism after being vaccinated, that is good evidence that vaccines can cause autism.” Researchers also tested people about their belief in conspiracy theories: “Important evidence about serious vaccine risks is being hidden from the public by a coordinated effort of health authorities and pharmaceutical companies.”

In all of these cases, the people who read the new CDC statement were more likely to believe these tropes, while people who read the old one were less likely to believe them.

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“It is always difficult to attribute changes in vaccination rates to one single factor,” says Böhm, “but in my view, this shift in CDC communication could indeed contribute to declining vaccine confidence and, ultimately, lower vaccination rates.”

Böhm and his colleagues aren’t the only ones looking at how people form opinions about vaccines. In a new study published in the journal Vaccine, researchers surveyed nearly 3,000 U.S.-based adults to determine where they get their daily news and whether that seemed to influence their views on vaccines. People who consumed news from the so-called “new right” media—including Breitbart, Newsmax, and ZeroHedge—were more than twice as likely to be vaccine hesitant as people who got their information from more mainstream or left-wing outlets.

“With public health becoming increasingly polarized, it’s critical to understand people’s attitudes about vaccines, and this work suggests people’s media preferences play an outsized role in influencing those attitudes,” said Amelia Jamison, an assistant research scientist at Johns Hopkins University and a co-author of the study, in a statement that accompanied its release. Other recent research supports a similar partisan divide when it comes to vaccine attitudes, with Republicans far less likely to support school vaccine mandates than Democrats.

Addressing vaccine hesitancy depends at least in part on messaging, which has changed with the administration in power—and can again. “Research has shown that communicating scientific consensus can strengthen trust in science,” Böhm says. “So if that communication changes, it can also change how people think about vaccines.”

If not, he warns, the country risks outbreaks of diseases that could have been prevented by the simple intervention of routine vaccination. “We should not imagine epidemics as something that only happens after vaccination rates collapse dramatically,” Böhm says. “For highly contagious diseases such as measles, even relatively small declines in vaccine confidence and uptake can create pockets of vulnerability.”

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