MONDAY, Feb. 24, 2020 (HealthDay News) -- Nearly 1 in 5 American adults has mistaken beliefs about vaccines, and misinformation is more common among those who rely on social media than on traditional media, a new study finds.

Researchers surveyed nearly 2,500 adults nationwide in the spring and fall of 2019, when the United States was dealing with its largest measles outbreak in decades, and found that up to 20% of respondents were at least somewhat misinformed about vaccines.

Eighteen percent mistakenly said it's very or somewhat accurate to say vaccines cause autism; 15% wrongly said it's very or somewhat accurate to say vaccines are full of toxins; 20% incorrectly said it's very or somewhat accurate to state that it makes no difference to delay or spread out vaccines instead of following the official schedule; and 19% incorrectly said it's very or somewhat accurate to state that it's better to develop immunity by getting a disease than by vaccination.

Between spring and fall, 19% had a significant change in levels of vaccine misinformation. Of those, 64% were more misinformed and 36% became better informed, the researchers reported.

Media sources used by the respondents had an impact on changes in misinformation levels. Those who relied more on social media for information about measles and the MMR (measles, mumps and rubella) vaccine were more likely to show misconceptions in the second survey.

However, misinformation fell among respondents who relied more on traditional media sources.

The study also linked low levels of trust in medical experts to believing vaccine misinformation.

And vaccine misinformation was persistent. Most respondents (81%) were just as informed or misinformed in the spring as they were in the fall, despite extensive news coverage of the measles outbreak and attempts by the U.S. Centers for Disease Control and Prevention to educate the public.

The study, by researchers at the Annenberg Public Policy Center of the University of Pennsylvania, was recently published in the Harvard Kennedy School Misinformation Review.

This high level of misinformation is "worrying" because it undermines vaccination rates, and high vaccination rates are needed to maintain community immunity, said study lead author Dominik Stecula, a postdoctoral fellow at the center, and his colleagues.

The findings are consistent with previous studies suggesting that misinformation about vaccination is more common on social media, while science-based information about vaccination benefits and safety is more common in traditional media, the researchers said in a university news release.

More information

The U.S. Centers for Disease Control and Prevention has more on vaccines and immunizations.