Vaccines Prove the Power of Positive Reinforcement

MIT researchers say that the more people know about vaccine acceptance by others, the more like they are to be vaccinated

MIT Initiative on the Digital Economy
4 min readMar 10, 2021


Public health officials have issued plenty of warnings about people who are reluctant to get vaccinated for Covid-19. But an MIT research team centered at MIT’s Initiative on the Digital Economy (IDE) says this may be counterproductive: When shown basic numbers about how popular Covid-19 vaccines are, the fraction of people reluctant to get the vaccine drops by 5 percent. To reach these conclusions, the team drew on a massive international survey about the pandemic, including 1.8 million responses from 67 countries, and developed an experiment covering 300,000 people in 23 countries. The researchers described their findings in a working paper and a recent LA Times op-ed. The MIT researchers are: Alex Moehring, Avinash Collis, Kiran Garimella, M. Amin Rahimian, Sinan Aral, and Dean Eckles.

MIT News talked to Aral and Eckles about the findings.

MIT IDE Director, Sinan Aral, (left) and Associate Professor Dean Eckles, speak about their new research.

Q: You have written that there is a “dangerous irony” in public health officials and other people highlighting those who are reluctant to get a Covid-19 vaccine. Why is that?

Eckles: It makes sense for public health officials and others to be worried about vaccine hesitancy, because we need a very high level of vaccine acceptance.

But a lot of the time, officials make it seem as if more people are hesitant than is really the case.

Many people who say they’re unsure if they’ll get the vaccine may be pretty easy to sway, and one way is by telling them, “Actually, a large fraction of people in your country say they’re going to accept the vaccine.” We found that simply by giving people accurate information about the percentage of people in their country who say they will accept a vaccine, it increased vaccine-acceptance intentions across 23 countries. Part of what’s exciting is how consistent this finding is.

Aral: I’d like to add three points. Before this study, there were at least two plausible countervailing hypotheses. One is that if more people heard that others would take the vaccine, the more they [themselves] would be inclined to take the vaccine. The other is that people would free-ride on the vaccine intentions of others: “Well, if they’re going to take it, they can create herd immunity and I can avoid taking a vaccine myself.” Our research shows pretty clearly that the first is true, while the second is not true [on aggregate].

Second, it’s interesting that the treatment most changes the behavior of people who are most underestimating the amount of vaccine acceptance among others. And third, there’s an overarching theme here: Simply providing people the truth, the accurate information, is also very effective at swaying people to accept the vaccine.

Q: What does this teach us about human behavior, at least in these kinds of situations?

Aral: One really important thing is [the power of] social proof. When you see large portions of people behave in a certain way, it legitimizes that behavior. And there are countless examples of this. When a lot of people say a restaurant is good, you’re swayed. This is another instance of that.

Eckles: There’s an informational process of social learning. People are trying to figure out: What’s the quality of this thing? It might seem weird to some of us following the news more, or watching what’s happening with [vaccine] trials, but a lot of people are not paying attention. They may know there are these vaccines, but even so, other people’s choices can be quite informative to them.

Q: What should be the core of good messaging about vaccination programs, based on your research over the last year?

Aral: As recently as February, a coronavirus task force started its communications by focusing on vaccine hesitancy. That is not, per our findings, as effective as leading with the vast and growing majority who are accepting. That’s not to say we think public health officials shouldn’t talk about vaccine hesitancy, or that people who are hesitant shouldn’t be targeted with outreach to convince them of the safety and efficacy of vaccines — we believe that should all happen.

Neglecting to emphasize the vast and growing majorities who are accepting vaccines doesn’t increase vaccine acceptance as much.

Eckles: What we’re saying is one part of a broader messaging strategy. Giving people this information is enough to shift their motivation to get the vaccine in a lot of cases. Though, getting them motivated is not enough if they don’t know what website to go to, or if it’s hard to get an appointment. It’s good to couple motivational messages with actionable information.

Aral: To our knowledge this is the largest global survey of Covid-19 behaviors, norms, and perceptions. We’ve been running it since July. We’ve also done many published studies, whether about social spillovers [during the pandemic], vaccines, vaccine misinformation — all of this is part of a very forceful effort by the Initiative on the Digital Economy to make meaningful contributions to changing the trajectory of this pandemic.

Originally published at on March 10, 2021.

Read more on MIT Sloan here.



MIT Initiative on the Digital Economy

Addressing one of the most critical issues of our time: the impact of digital technology on businesses, the economy, and society.