Want a chance to win millions of dollars? A college scholarship? A free shotgun? All you have to do is get vaccinated against COVID.

As vaccination rates have slowed, a growing number of states, companies and organizations have started offering incentives ranging from cash giveaways to free beer. The need to promise such rewards in exchange for protection against a deadly disease may seem baffling—especially when so many people around the world lack access to vaccines entirely. But the medical community has a long history of using inducements to get individuals to take actions for the good of society.

“I think that incentivization for a desired public health behavior is absolutely appropriate and has been actually shown to be already [effective] in the vaccine campaign,” says Monica Gandhi, a professor at the University of California, San Francisco, School of Medicine, who has a lot of experience using incentives to encourage healthy behaviors within the HIV community. “Beer, doughnuts, $1-million lottery tickets—it’s just human behavior.”

Ohio was among the first of several states to offer a cash lottery for residents who get a COVID vaccination. Its Vax-a-Million program is awarding a total of five $1-million prizes for Ohioans age 18 and older who have gotten at least one vaccine dose. Ohio is also offering 12- to 17-year-olds chances at five full scholarships to any college or university in its state system. Less than a week after the program was announced, the Ohio Department of Health said vaccination rates had jumped by 28 percent.

New York State is giving away scratch-off lottery tickets with a $5-million grand prize to adults who get their shot at one of its designated mass vaccination sites. And it is giving 12- to 17-year-olds tickets for weekly random drawings for a full scholarship to colleges in the State University of New York or City University of New York system. The state is also offering a seven-day unlimited-use subway card or two train tickets to people who get vaccinated at one of the walk-up sites at New York City stations. And the city is giving out free tickets to local attractions, such as New York City Football Club and the Statue of Liberty.

California’s Vax for the Win program has been awarding a total of $116.5 million in prizes to residents who have gotten at least one vaccine dose. Thirty of these winners were selected for big-payout “$50,000 Fridays” during the first two weeks of June. And 10 Californians were selected to receive $1.5 million each on June 15. To claim their prizes, participants must complete their vaccination process (for those who had received one dose of a two-shot vaccine). Additionally, the state has been giving out $50 prepaid cards or grocery gift certificates to the first two million people to get vaccinated starting on May 27.

Other states are taking even more creative approaches to persuading the unvaccinated. West Virginia is holding a lottery with hunting rifles and shotguns as prizes. New Jersey and Connecticut gave away free beer and other beverages. In May Alabama offered people who had been vaccinated or gotten a COVID test the chance to drive on its famous Talladega Superspeedway. And Washington State recently began allowing retailers to offer people a free cannabis joint in exchange for getting vaccinated.

Private companies are getting in on the incentive craze, too: Back in March Krispy Kreme began giving away doughnuts to those who show their official COVID vaccine card. Health care company CVS Health is offering customers who get vaccinated at one of its pharmacies or other outlets the chance to win free trips, cruises, VIP tickets and travel to the Super Bowl, and other prizes.

“When we think about human behavior and people’s decision-making, there are two main approaches: you can have incentives, or carrots, and you can have sticks, or penalties,” says Karen Sepucha, director of the Health Decision Sciences Center at Massachusetts General Hospital’s general medicine division. She notes that public health experts use incentives all the time to get people to quit smoking, exercise more, and so on.

In the first phase of COVID vaccination, demand was high, and people were desperately vying for limited appointments. Now that vaccines are widely available, those who remain unvaccinated fall into roughly two groups: one is on the fence about getting vaccinated, and the other fundamentally opposes it. “The idea of using incentives to get that middle group over that hump and nudge them along is a very reasonable idea that has definitely worked in the past for these sorts of short-term, concrete activities that we want to incentivize people to do,” Sepucha says.

In a study that has not yet been published, Sepucha, Lynn Vavreck, a professor of politics and public policy at the University of California, Los Angeles, and their colleagues tested how well various incentives might work for COVID vaccination. They surveyed a sample of tens of thousands of people who were not vaccinated and had not yet scheduled an appointment about their willingness to do so under different circumstances. In one experiment, the researchers randomly assigned participants to several groups and asked them how likely they would be to get vaccinated if they received a cash reward, with amounts ranging from $25 to $100. In another experiment, the scientists asked people the same question—but instead of a cash reward, some were told they would no longer have to wear a mask or social distance after being vaccinated, whereas others were told they would have to continue these behaviors.

About a third of the people asked about a cash reward said they would be more likely to get vaccinated if they received it, and the percentage who expressed willingness increased with the amount of money. The prospect of not needing to wear a mask or follow social-distancing guidelines also increased people’s self-reported willingness to be vaccinated. Interestingly, participants who identified as Democrats were slightly more likely to respond to the cash reward, whereas self-declared Republicans were slightly more likely to be swayed by the lifting of behavioral restrictions.

The findings are in line with a recent CNN report that found that interest in vaccination increased after the U.S. Centers for Disease Control and Prevention announced that vaccinated people would no longer need to wear masks in most situations.

“People are motivated by different things. One incentive isn’t going to work for everyone,” Sepucha says. Also, such rewards only work to a certain extent, Vavreck notes. They can, for example, help sway the set of people who say they simply want to see how well the vaccines work on others before they will feel comfortable rolling up their own sleeve. But some people—including many of those who strongly distrust authorities—will always oppose vaccination. “No amount of money is likely to change someone’s mind [if they think] that the government is up to no good,” Vavreck says.

The risk-benefit calculation of getting vaccinated is also different for younger people, who are less likely to become seriously ill if they get COVID. Some colleges are requiring students to be vaccinated before coming to campus in the fall. That is one way to do things, Gandhi notes. Alternatively, she says, colleges could make vaccination optional but entice students with promises of normality. “You could say, ‘Guess what, life’s going to be normal,’” she adds. “‘You don’t have to mask. You can hang out and have as many parties as you like.’”

Many employers have offered workers hefty incentives to get vaccinated, and some are making it a requirement. But a few of the latter are already drawing a backlash.

Gandhi says she does not believe mandates are the ideal approach to getting people vaccinated. “I just think positive motivating behavior is the way to get to get where we need to be,” she says.