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Study: To boost immunization rates, emphasize vaccine acceptance

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Stopping the COVID-19 pandemic hinges on people opting to get a vaccine, as it can be difficult to reach herd immunity even with a majority of people getting a vaccine. Public health messaging that emphasizes that others are getting a COVID-19 vaccine makes people more likely to get a vaccine themselves, according to a new study co-authored by MIT Sloan professorsand

“While public health officials and the media have been emphasizing the potential negative impact of vaccine hesitancy, our study found that emphasizing the overwhelming vaccine acceptance expressed by most people is a better way to get those who are unsure to accept COVID-19 vaccines,” said Aral, who is the director of the MIT Initiative on the Digital Economy.

The preliminary paper, “Surfacing Norms to Increase Vaccine Acceptance,” was co-authored by MIT Sloan PhD student Alex Moehring, postdoctoral researcher Kiran Garimella, M. Amin Rahimian from the University of Pittsburgh, and Avinash Collis from the University of Texas. It is under peer review.

There is growing evidence that people’s preventative health behaviors — like getting vaccinated — are “dramatically” influenced by social and cultural factors, the researchers wrote. (Other studies, conducted by Aral, Eckles, and others at the MIT IDE, have found that people’s behavior during COVID-19 has been affected by factors such as the behavior of their connections, including those they connect with over social media.)

Unlike other observable preventative behaviors, like wearing masks, people might not know whether others intend to get vaccinated. As a result, messaging about this could have especially large affects, the researchers write. Before the release of this study, it was not clear whether learning that a large majority of the population is getting the vaccine would motivate people to get vaccinated themselves, or whether it might decrease acceptance because people assumed that if others got it, they wouldn’t have to.

Learning about vaccine acceptance and other COVID-19 behaviors motivated Aral and Eckles to launch the world’s largest longitudinal study about COVID-19 beliefs, behaviors, and perceptions, in collaboration with Facebook, Johns Hopkins University, and the World Health Organization. The survey has collected responses from more than 1.6 million people since July 2020. According to Eckles and Aral, their survey shows that over the last four weeks about 70% of adults in the United States plan to accept a vaccine or have already received one. More than 13% said they “don’t know” if they will accept one.

For the experimental study about health messaging, the researchers randomized the survey for a subset of more than 300,000 people in 23 countries who were asked about their vaccine intentions. The researchers provided information about the behavior of others at various times during the survey.

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The study showed that accurate information about the behavior of others can increase people’s intentions to accept a COVID-19 vaccine. When those surveyed were given accurate information about the number of people who said they would get the vaccine, the amount of people who said they were unsure or felt negative about accepting a vaccine was reduced by 5%.

The change in views about vaccine acceptance can be at least partially explained by changes in respondents’ beliefs about the descriptive norms — the things people do, believe, or say because they believe other people do, believe, or say them too — around the vaccine. This suggests that public messaging should avoid overemphasizing the hesitation some people have about vaccines. 

“Humans are sensitive to the behaviors of others. Public health communications should avoid overemphasizing the shrinking minority of people who say they won’t accept a vaccine against COVID-19,” Eckles said. “The best way forward, as is often the case, is the presentation of clear, accurate, and timely information. That includes the information that other people overwhelmingly intend to accept these vaccines.”

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