Maryland officials have hailed the state’s $2 million VaxCash lottery as an “unqualified success,” a promotion that helped the state reach its goal of inoculating 70 percent of its adult population with at least one shot of a coronavirus vaccine by Memorial Day.

It worked so well at boosting vaccinations that they decided to start another one: VaxU Scholarship, which offers 20 vaccinated 12- to 17-year-olds a chance at winning a $50,000 in-state public college scholarship. It runs until Labor Day.

“There are some people who just either haven’t gotten around to it or they are like, ‘I may get it, but I just didn’t feel the need,’­ ” Gov. Larry Hogan (R) said in early July at the launch of the VaxU Scholarship. “There are others who are just opposed to it and are hard to convince. But I think there are more of the folks that just need a little extra incentive to go out and do it, and I’m hoping that this opportunity at a college scholarship and us getting out talking about the importance of it will help encourage some more younger people to do so.”

Although state officials say the incentives have helped Maryland become one of the most vaccinated states in the country, it remains unclear how significant a role the lottery played in motivating people to get vaccinated or whether the state could have reached its goal without it.

“Money can be a powerful motivator, but the key word there is ‘can,’ ” said Joshua Liao, a doctor and behavioral scientist at the University of Washington. “But people get vaccinated for a variety of different reasons.”

Some experts, including one who studied the first cash vaccination lottery in Ohio, have questioned whether the jackpots lead to more inoculations. And one Maryland winner even speculated about whether the incentives might have the opposite effect.

At least a dozen states have given away or plan to award seven-figure cash lottery prizes to encourage people to get vaccinated. Many of the incentive programs, such as VaxU Scholarship, continue as the delta variant — which spreads about two to three times as fast as the original variant of the coronavirus — poses a new threat for the unvaccinated.

Under California’s $116 million Vax for the Win, the country’s largest pot of vaccination incentive money, residents are receiving prizes including a $50 gift card, a “dream vacation” to a California city and a $1 million prize. New York gave away lottery scratch-off tickets to residents who got vaccinated at a state-run vaccine clinic during the program, which ran in late May. And Ohio offered $1 million weekly prizes and full-ride college scholarships.

As of mid-July, D.C. health officials said they had given out more than 2,000 of its $51 gift cards and more than 300 gift cards to people who brought other people to get vaccinated. City officials say they believe the incentives are worth trying, especially if they nudge some people into receiving a shot. Last week, they announced a new lottery to boost vaccinations among 12- to 15-year-olds.

On May 13, the week before the VaxCash lottery was announced in Maryland, the seven-day rolling average of adults who received an initial dose of a vaccine was 14,800. On May 27, a week after the promotion, it was 10,900, according to state health department data.

Michael Ricci, a spokesman for Hogan, said officials never expected to see an uptick in vaccinations, largely because so many people were already vaccinated when the promotion began.

On April 20, a month before the announcement, about 2.7 million people had received at least one dose of a vaccine. By the time of the announcement, that number had grown to 3.4 million. A month later, on June 20, it had risen to nearly 3.7 million.

The state’s goal, Ricci said, was to hit 70 percent of adults with at least one vaccine dose by May 28. President Biden set a similar goal for the country by July 4 but failed to reach it. Meanwhile, Maryland hit a new goal of vaccinating 75 percent of its adult population by July 4, and as of Thursday, 77.1 percent of adults had received at least one shot.

“Our average of daily doses administered relative to population jumped to first in the nation in the period after the announcement,” Ricci said in an email. “Another metric of success is that we both held and gained ground in the national rankings over the course of the lottery.”

Other states — including Virginia, where 71.9 percent of the adult population has received at least one vaccine dose — have opted not to offer big cash lottery incentives. Virginia officials have questioned whether million-dollar lotteries are the best long-term strategy to reach herd immunity.

When Hogan announced the first lottery, which offered $40,000 checks daily for 40 days and ended with a $400,000 grand prize on July 4, 67.3 percent of Maryland residents 18 and older had received at least one dose of a vaccine.

The prize was offered to any adult who was vaccinated, regardless of when the vaccine was administered.

Hogan said the lottery was part of the state’s mission to ensure that “no arm is left behind.”

“We’re using every resource at our disposal to achieve that goal,” he said at the announcement, alongside a man in a Maryland lottery ball costume. “Promotions like this are just one more way that we are reinforcing the importance of getting every single Marylander we can vaccinated against covid-19.”

The promotions highlight the challenges that states face in trying to persuade people to get vaccinated.

Gerard Dupree, who won one of the more than three dozen $40,000 checks that Maryland awarded, said he isn’t convinced that giving money and other rewards — such as free pizzas, gift cards and cars — to get a shot works. It hasn’t among some of his family and friends who are still unvaccinated.

Before he got vaccinated, Dupree said, he heard of a group in D.C. offering a free cannabis promotion, “Jabs for Joints,” which only made him suspicious about the vaccines.

“People were thinking, ‘Why are they so pressed to give people incentives to take the vaccine?’ ” he said. “For people who have mistrust, it just makes you more suspicious.”

Dupree, who lives in Anne Arundel County, received his initial dose at the end of April, before the lottery was launched. He decided to get vaccinated after contracting the virus more than a month earlier.

Before getting the coronavirus, Dupree said, he was against getting vaccinated. He figured he was healthy and he didn’t need it. Plus, he said, like many of his friends and family, he didn’t trust what government officials were saying about covid or the necessity of getting vaccinated.

“Once I felt the symptoms, I said I need to be done with that,” said Dupree, 61. “I felt like it was better for me to get the vaccine. I’d rather deal with the side effects of the vaccine than to deal with the virus.”

Allan J. Walkey, a professor of medicine at the Boston University School of Medicine who studied the effect of the Ohio cash lottery program and published an article for the Journal of the American Medical Association, found that daily vaccination rates slowed in Ohio and across the country after the Ohio lottery was introduced in mid-May.

Walkey said most people got their shots before the lottery was announced, and as a result, most of the prizes were awarded to those who were already vaccinated, which made it more of a reward for the vaccinated rather than a stimulus for people to get a shot.

“I think it was a good try and probably worth an initial effort,” he said, “but continuing to try lotteries at this point is not going to be beneficial.”

Walkey’s work focused on cash lotteries for adults. He said it did not look at whether scholarships would drive 12- to 15-year-olds to get vaccinated.

Ricci said the state has seen an uptick in vaccinations among 12- to 17-year-olds since the scholarship announcement.

“We expect that trend to continue, especially as we head into back-to-school season,” he said.

Julie Zauzmer contributed to this report.