Doctor or nurse giving shot or vaccine to a patient's,Vaccination and prevention against coronavirus pandemic,Vaccination of the population against diseases concept.
CNN  — 

Vaccine misinformation, which first began spiraling during the Covid-19 pandemic, has grown in the United States in the years since, according to a new survey from the Annenberg Public Policy Center of the University of Pennsylvania.

More than 1,500 adults responded to the survey between October 5 – 12 and according to the results, the share of people who viewed vaccines as less safe and effective has increased since April 2021, when the group was first included on a panel for the survey.

Americans are less likely to consider it safe to get the measles, mumps and rubella (MMR), pneumonia and Covid-19 vaccines than they were in April 2021.

While still a small group, people with views about the vaccines causing autism, cancer and illnesses such as the flu or Covid-19 also ticked up.

The percentage of Americans who believe that vaccines are approved for use in the US are safe dropped 6 percentage points since April 2021 to 71%, while the share of adults who don’t think the approved vaccines are safe nearly doubled in the same time frame – increasing from 9% to 16%.

“There are warning signs in these data that we ignore at our peril,” said Kathleen Hall Jamieson, director of the Annenberg Public Policy Center and director of the survey, in a news release. “Growing numbers now distrust health-protecting, life-saving vaccines.”

Jamieson told CNN in an email that she was surprised by the data.

“Instead of plateauing, levels of misinformation increased as the pandemic was winding down,” she said, noting that, “For a worrisome part of the population, the rhetoric surrounding COVID vaccination increased acceptance of misinformation and decreased confidence in vaccines.”

For example, the share of people who thought “increased vaccines are why so many kids have autism these days,” grew from 10% in April 2021 to 16% last month.

Despite several studies finding no association between vaccines and autism, the myth of a link continues to be spread by anti-vaccine activists.

The Biden administration has worked to combat health misinformation. In 2021, US Surgeon General Dr. Vivek Murthy said it posed “a serious threat to public health” in a 22-page advisory that urged individuals to take responsibility for limiting the spread of misinformation.

“Health misinformation is a serious threat to public health. It can cause confusion, sow mistrust, harm people’s health, and undermine public health efforts. Limiting the spread of health misinformation is a moral and civic imperative that will require a whole-of-society effort,” he said.

Experts say misinformation contributes to vaccine hesitancy and emphasize the importance of meeting people where they are by being able to explain the biology of the immune system and why hesitations about overwhelming the immune system don’t need to be a concern.

Get CNN Health's weekly newsletter

Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.

There are other factors too, that can influence whether people choose to get vaccinated, Jamieson said. For example, “Past vaccination predicts future vaccination.”

“Reliance on mainstream media sources is associated with higher trust in public health experts, higher levels of knowledge about vaccination, and higher levels of reported COVID-19 vaccination,” Jamieson said, adding that having more information about how safe past vaccines are, or awareness of the levels and stages involved in the approval process by the US Food and Drug Administration and the US Centers for Disease Control and Prevention can also boost willingness to get vaccinated.

In 2021, the US Department of Health and Human Services published a Community Toolkit on health misinformation that provides guidance for people who see or hear health-related content that they aren’t sure about.

The agency advises checking with your health care provider, the CDC or your local public health department to see whether there might be any truth to the claim.

You can also search online to see if the claim has been verified by a credible source such as government agencies or peer-reviewed medical journals.

At the end of the day, HHS said, if you aren’t sure about content you see online, do not share it with others

CNN’s Deidre McPhillips and Amanda Muse contributed to this report.