While researchers around the world are developing vaccines for COVID-19, in the coming months governments will face another major obstacle: getting people to actually take them.

In one recent poll, roughly one in three Americans said they would reject a vaccine even if it was approved by the Food and Drug Administration and available for free. Another survey suggested that only half of Americans would definitely agree to be vaccinated. A survey in the United Kingdom found that just 30 percent of respondents were certain they will take a COVID-19 vaccine. (Another 43 percent said they were either very likely or fairly likely to take one.)

“I am worried that the vaccination rate is not going to be as high as everyone expects,’’ said Mitesh Patel, a physician and a professor of medicine at the University of Pennsylvania.

Vaccination in large numbers — perhaps 60 to 70 percent of the population — is crucial to develop herd protection and sever the chains of transmission from one person to another, particularly those who are most vulnerable.

That’s why experts in the behavioral and psychological sciences are thinking of ways to nudge people into doing the right thing.

Nudges — which are generally cheap, subtle, and quick interventions — first came under the spotlight in a 2008 book by American scholars Richard Thaler and Cass Sunstein. Thaler went on to win the 2017 Nobel Prize in economics for his contributions to behavioral economics.

Governments and other institutions have nudged people in a variety of scenarios: by painting flies on the inside of urinals to encourage cleanliness, for example, or by drawing baby faces on shop shutters to discourage violence and theft. The nudge theory has, however, attracted some criticism for the implicit assumption that experts know what’s in the interest of ordinary people more than the people themselves.

Effective nudges for COVID-19 could make vaccination the default — something expected of people unless they actively opt out. That would exploit the psychological tendency for people to feel more responsible for bad outcomes that result from their actions than they do for bad outcomes that result from inaction, said Alberto Giubilini, a bioethicist at the University of Oxford.

Regularly reminding people to get vaccinated has been shown to increase vaccine uptake, at least modestly, said Noel Brewer, who studies health behavior at the University of North Carolina. Medical centers also could send their patients vaccination appointment notifications with times and dates already set, instead of asking them to choose days and times. That’s been useful in boosting flu vaccination rates.

Another possible intervention, Brewer noted, could be to vaccinate children at school without requiring parental authorization but allowing parents to opt out if they object. Evidence suggests that parents are significantly less likely to resist having their children vaccinated under this presumptive approach. Monetary incentives may also be an option.

Giubilini said that ideally, the COVID-19 vaccine would be compulsory, with legal penalties for noncompliance. But since that would likely draw outcry and resistance from skeptics, nudges are ideal, because they would preserve freedom of choice.

There’s just one caveat: Public confidence is necessary for nudges to work, Brewer said, and the COVID-19 vaccine is being developed at the fastest rate of any vaccine in history. “Efforts to rush along a vaccine or cut corners are going to undermine people’s confidence in vaccination,’’ he said, “and as a result, they’re going to undermine our ability to put in place all the programs that we know are very effective.’’

— Dalmeet Singh Chawla, a science journalist in London. Follow him on Twitter @DalmeetS.