promoting inoculations, and stadiums have become a new line of demarcation, where vaccinated sections are highlighted as perks akin to V.I.P. skyboxes.

In Washington, Gov. Jay Inslee recently announced that sporting venues and churches would be able to increase their capacity by adding sections for the vaccinated.

Some businesses — like gyms and restaurants — where the coronavirus was known to spread easily are also embracing a reward system. Even though many gyms have reopened around the country, some still haven’t allowed large classes to resume.

Others are inclined to follow the lead of gyms like solidcore in Washington, D.C., which seeks proof of inoculation to enroll in classes listed as “Vaccine Required: Full Body.” “Our teams are now actively evaluating where else we think there will be client demand and will be potentially introducing it to other markets in the weeks ahead,” said Bryan Myers, chief executive officer of the national fitness studio chain, in an email.

specific invitation designs with the inoculated in mind, vaccinated only please RSVP.

Not everyone endorses this type of exclusion as good public policy. “I worry about the operational feasibility,” said Jennifer Nuzzo, an epidemiologist at the Johns Hopkins Coronavirus Resource Center. “In the U.S., we don’t yet have a standard way to prove vaccination status. I hope we’ll see by fall such low levels of infection in the U.S. that our level of concern about the virus will be very low.”

But few dispute that it is legal. “Having dedicated spaces at events reserved for vaccinated people is both lawful and ethical,” said Lawrence O. Gostin, an expert in health law at Georgetown Law School. “Businesses have a major economic incentive to create safer environments for their customers, who would otherwise be reluctant to attend crowded events. Government recommendations about vaccinated-only sections will encourage businesses and can help us back to more normal.”

so far to impose vaccine mandates for workers, especially in a tight labor market. “Our association came out in favor of masks,” said Emily Williams Knight, president of the Texas Restaurant Association. “We probably will not be taking a position on mandates, which are incredibly divisive.”

But some companies are moving that way. Norwegian Cruise Line is threatening to keep its ships out of Florida ports if the state stands by a law prohibiting businesses from requiring vaccines in exchange for services.

Public health mandates — from smoking bans to seatbelt laws to containing tuberculosis outbreaks by requiring TB patients to take their medicines while observed — have a long history in the United States.

“They fall into a cluster of things in which someone is essentially making the argument that what I do is only my business,” said Dr. Frieden, who is now chief executive of Resolve to Save Lives, a program designed to prevent epidemics and cardiovascular disease. “A lot of times that’s true, unless what you do might kill someone else.”

Dr. Frieden was the main official who pushed for a smoking ban in bars and restaurants in 2003 when he was the New York City health commissioner under former Mayor Michael R. Bloomberg. Other senior aides at the time felt certain the ban would cost Mr. Bloomberg a second term. “When I was fighting for that, a City Council member who was against the ban said of bars, ‘That is my place of entertainment.’ And I said, ‘Well, that’s someone’s place of employment.’ It did have impact.”

Mr. Duggan, the bar owner in Washington, said protecting his workers and patrons are of a piece. “As we hit a plateau with vaccines, I don’t think we can sit and wait for all the nonbelievers,” he said. “If we are going to convince them, it’s going to be through them not being able to do the things that vaccinated people are able to do.”

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