In his eastern Maryland congressional district, conservative GOP Rep. Andy Harris is vaccinating his constituents against COVID-19.

He’s part of a cohort of physicians-turned-lawmakers on Capitol Hill volunteering to give shots to Americans in their communities, as part of the broader effort to bring the country closer to herd immunity.

The work of Harris, an anesthesiologist by training, Rep. Brad Wenstrup of Ohio, and other members of the GOP Doctors Caucus is particularly important given the high rate of vaccine hesitancy observed in conservative Americans.

According to a recent Quinnipiac University poll, 45% of Republicans said they do not plan to get a COVID-19 vaccine, compared to 27% of Americans surveyed overall.

“Republicans are more skeptical of government; when the government comes out and says, we think you ought to take the vaccine, some people’s natural reaction is, ‘let me think about that,'” Harris told ABC News. “They hesitate a bit.”

The United States over the weekend reached the milestone of administering at least one vaccine dose to half of all American adults, according to the Centers for Disease Control and Prevention. But vaccination rates have lagged in red states including Mississippi, Alabama, Louisiana and Tennessee, where fewer than 40% of adults have received at least one dose, according to the Associated Press.

“We’re seeing real hesitancy in certain groups, mostly Republicans, who fear the concerns around the vaccine or maybe downplay the risks around the pandemic,” Dr. John Brownstein, an epidemiologist at Boston Children’s Hospital and Harvard Medical School and an ABC News contributor, said in an interview.

The country’s ability to reach herd immunity from COVID-19 could be jeopardized, he said, if some communities continue to hold out against vaccines.

“We need to be looking at the country as a whole, but if we’re going to get this virus under control, we’re going to need people across communities,” Brownstein said.

The single-shot Johnson & Johnson vaccine had been developed using a more traditional approach than the MRNA vaccines produced by Pfizer and Moderna, but the federal government recently ordered a pause on distribution and administration of the vaccine after six people of the nearly 7 million who received the vaccine in the U.S. developed rare blood clots, the cause of which are still being investigated.

Harris said the pause may “add a little skepticism,” but predicted that Americans will “get over it.”

“People are going to realize, you know, these are one-in-a-million events. They’re very, very unusual. You’re more likely to get injured in a car accident on the way to the clinic than to have this problem occur. So I’m hoping that people get over that skepticism,” he said, adding that he believes more conservatives will opt to get vaccinated once they see friends and family take their own shots.

Rep. Mariannette Miller-Meeks, R-Iowa, a freshman lawmaker who served as Iowa’s top public health official for four years, said her dual role as a doctor and lawmaker helps her connect with constituents on taking the vaccine.

“There was an elderly couple coming in and they were of such an age that I would have thought they’d already been vaccinated,” she told ABC News. “I asked them if they’re getting vaccinated. And they said they were very nervous. They were very anxious. And I said, well, how would how would you feel if I gave you your vaccine? And they said, that would be great. And so it was just this matter of calming them down, reassuring them, talking them through.”

The White House has also been working on outreach to conservative voters and red states, launching promotional and advertising campaigns with NASCAR, Country Music Television, and other outlets to “get directly connected to white conservative communities,” press secretary Jen Psaki recently said in a press briefing.

Former President Donald Trump, who decided to get the vaccine privately at the White House in January — though his predecessors and successor did so in public and on camera — has also urged his supporters to get vaccinated.

“I would recommend it to a lot of people that don’t want to get it and a lot of those people voted for me, frankly,” he said in a Fox News interview in March. “It’s a great vaccine, it is a safe vaccine.”

Rep. Brad Wenstrup, R-Ohio, the chair of the GOP Doctors Caucus, told ABC News that Americans “really need to hear more from doctors who are treating patients,” rather than politicians, in order to foster more trust in the vaccine among conservatives.

“Most people want the one-on-one, they want it explained to them,” Wenstrup, who has also vaccinated Ohioans in his capacity as an Army Reserve officer, told ABC News.