BOSTON — Massachusetts awarded its first $1 million prize to a vaccinated adult this week in the opening drawing of VaxMillions, a game that aims to persuade the reluctant to get their shots to ward off COVID-19.

But the allure of cash doesn’t appear to have significantly boosted vaccination rates, which are declining, according to state health data.

And nearly half of those eligible for the sweepstakes had not registered for the drawing.

The first round of the five-part game that awards $1 million prizes to fully vaccinated adults, and $300,000 college scholarships to vaccinated children, were announced Thursday.

The cash went to Darrell Washington, a 63-year-old Blue Cross Blue Shield case worker, while the scholarship was awarded to Daniela Maldonado, a 15-year-old high school sophomore who says she’s from a low-income family and aspires to the University of Massachusetts or Boston University.

“Today is a pretty big day,” Gov. Charlie Baker said in announcing the winners.

But in the build-up to the drawing, fewer than half of those who are fully vaccinated had actually registered. And the rate of new vaccinations being given was slowing.

Massachusetts counted 53,177 doses administered last week — down 14% from the previous week, according to the state Department of Public Health.

Meanwhile, the state has one of the highest vaccination rates for COVID-19 in the country: More than 4.3 million people in Massachusetts, or about 64% of the total population, are fully vaccinated.

There will be four more weekly drawings, and those who’ve yet to get vaccinated still have until Aug. 19 to get jabbed and register for a chance to win.

Baker has defended the sweepstakes.

“Somewhere in the vicinity of 300,000 shots have been delivered since that program was put in place,” he told reporters. “And we continue to see a very robust number of people getting vaccinated every day.”

The chances of winning VaxMillions, at this point, are still better than the chances of winning the state lottery.

But the declining numbers of shots has raised questions about whether the sweepstakes is worth the cost to the state, which is using federal pandemic relief funds to cover the prizes and administrative costs.

Other states have implemented similar giveaways to entice people to get vaccinated.

Dr. David Hamer, a professor at Boston University’s School of Public Health and School of Medicine, said it’s not yet clear if VaxMllions is succeeding.

”The hope was that it might spur on some of those people, but if they are seriously vaccine hesitant, these kinds of incentives won’t be enough to convince them,” he said. “This is sort of the hard-core of those who are unvaccinated.”

He said reasons for hesitancy range from concerns about safety and side effects, to a lack of trust.

For those people, he said, it will take more than dangling cash to get them vaccinated.

Christian M. Wade covers the Massachusetts Statehouse for North of Boston Media Group’s newspapers and websites. Email him at cwade@northofboston.com