The U.S. vaccination story varies widely across regions.

Almost half of Americans have received at least one dose of a Covid-19 vaccine. But the U.S. vaccination story varies widely across regions, with New England surging ahead of the national average and much of the South lagging far behind.

In five of the six New England states, more than 60 percent of residents are at least partly vaccinated, according to data from the Centers for Disease Control and Prevention. It’s a different story in the South, where Mississippi, Alabama, Arkansas, Georgia, Louisiana and Tennessee have the country’s lowest rates of residents who have received at least one shot. The rates in those states are all below 40 percent, with Mississippi, at 33 percent, at the bottom of the list.

The White House and state governments, after relying on mass vaccination sites for months, are turning their focus to more targeted, smaller-scale efforts to vaccinate underserved, harder-to-reach communities.

“This next phase of the vaccination campaign was — will be driven, more than anything, by the people and organizations and communities who help to vaccinate their families, their friends and others in their neighborhoods,” Dr. Vivek Murthy, the surgeon general, said on Friday during a White House news conference. “It’s why we’ve been saying that addressing access, motivation and vaccine confidence requires an all-hands-on-deck approach.”

That strategy has been employed by Dr. John B. Waits, the chief executive of Cahaba Medical Care, which has 17 clinics in underserved communities in Alabama.

“Conversations with people you trust have always been important to us,” he said on Friday. “I’ve been on Facebook Live. I say: ‘Ask us the hard questions. Let’s talk.’ We pivot to the individual exam room, where they trust me to answer. We’re having success with that approach, but it’s not at the speed that the pandemic needs.”

The low rate in the South worries Thomas A. LaVeist, an expert on health equity and dean of the School of Public Health and Tropical Medicine at Tulane University in New Orleans.

“You have the carrot and stick,” he said. “I’m beginning to think that the stick is the more likely scenario.”

Dr. LaVeist said the incentive that would work fastest for adults would be mandates by employers, who are uniquely positioned to require large numbers of Americans who otherwise would not receive a vaccination to do so because their employment depends on it. The federal government has issued guidance that says employers can require workers to get a Covid-19 vaccine and bar them from the workplace if they refuse.

Dr. Murthy cited a Kaiser Family Foundation survey that found 28 percent of those who were employed said they would be more likely to get vaccinated if they were given time off to receive and recover from the vaccine. Another 20 percent said they would be more likely to get vaccinated if their shot was administered at their workplace. The survey looked at those who are unvaccinated but wanted to get a vaccine as soon as possible.

Dr. LaVeist and other experts, however, say the biggest hurdle among the vaccine hesitant is anxiety over possible side effects. “How was it possible to deploy the vaccine so quickly? If more people understand that, then more people will take the vaccine,” Dr. LaVeist said. “Corners were not cut.”

A recent New York Times report from Greene County, a rural area in northeastern Tennessee, revealed the most common reason for vaccine apprehension was fear that the vaccine was developed in haste and that long-term side effects were unknown. These decisions are also entangled in a web of views about autonomy, science and authority, as well as a powerful regional and somewhat romanticized self-image: We don’t like outsiders messing in our business.

Vaccine hesitancy in any U.S. region poses a threat to all Americans, experts warn, because the longer it takes to vaccinate people, the more time that the virus has to spread, mutate and possibly gain the ability to evade vaccines.

“My big concern is that there is going to be a variant that’s going to outsmart the vaccine,” Dr. LaVeist said. “Then we’ll have a new problem. We’ll have to revaccinate.”