WASHINGTON — Republican politicians are under increasing pressure to speak out to persuade COVID-19 vaccine skeptics to roll up their sleeves and take the shots as a new, more contagious variant sends caseloads soaring. But after months of ignoring — and, in some cases, stoking — misinformation about the virus, new polling suggests it may be too late to change the minds of many who are refusing.

In recent news conferences and statements, some prominent Republicans have been imploring their constituents to lay lingering doubts aside. In Washington, the so-called Doctors Caucus gathered at the Capitol for an event to combat vaccine hesitancy. And in Alabama, Republican Gov. Kay Ivey voiced exasperation as she pleaded with residents to protect themselves.

“Folks are supposed to have common sense,” she told reporters. “It's the unvaccinated folks that are letting us down. ... I've done all I know how to do. I can encourage you to do something, but I can't make you take care of yourself.”

The pleas come as COVID-19 cases have nearly tripled in the U.S. over the last two weeks, driven by the explosion of the new delta variant, especially in pockets of the country where vaccination rates are low. Public health officials believe the variant is at least twice as contagious as the original version, but the shots appear to offer robust protection against serious illness for most people.

Nearly all COVID-19 deaths in the U.S. are now people who haven't been vaccinated. Just 56.2% of Americans have received at least one vaccine dose, according to the Centers for Disease Control and Prevention.

“I think they've finally realized that if their people aren't vaccinated, they're going to get sick, and if their people aren't vaccinated, they're going to get blamed for COVID outbreaks in the future,” said GOP pollster Frank Luntz, who has been working with the Biden administration and public health experts to craft effective messaging to bring the vaccine hesitant off the fence.

But Luntz, who conducted another focus group Wednesday evening with vaccine holdouts, said there has been a discernible shift in recent weeks as skepticism has calcified into hardened refusal.

“Once you are opposed, it is very hard to change that position. And that's what's happening right now,” he said.

Indeed, a new poll from The Associated Press-NORC Center for Public Affairs Research found that most Americans who haven't been vaccinated say they are unlikely to do so, with 45% saying they definitely will not and 35% saying they probably won't. Republicans, the poll found, remain far more likely than Democrats to pass on the shots.

Overall, 83% of Democrats but only 51% of Republicans said they had received at least one dose. And among unvaccinated Republicans, just 12% said they were planning to get the shot, while 32% said they probably wouldn't, and 56% said they definitely won't.

For months now, many conservative lawmakers and pundits have been stoking vaccine hesitancy, refusing to take the shots themselves or downplaying the severity of the virus. Republican governors have signed bills protecting the unvaccinated from having to disclose their status and tried to roll back mask mandates. And on social media, disinformation has run rampant, leading President Joe Biden to claim platforms like Facebook were “killing people” — a claim he later walked back.

At a recent conservative gathering, attendees cheered the news that the Biden administration was falling short of its vaccination goals. Invoking the nation's top infectious-disease expert, Dr. Anthony Fauci, Rep. Lauren Boebert, R-Colo., warned the government: “Don't come knocking on my door with your Fauci Ouchie! You leave us the hell alone.”