The United States is at an unprecedented juncture of the pandemic, where slightly more than half the U.S. population is fully vaccinated, health and safety restrictions are looser than they have been in 18 months, and cases of new coronavirus infections are rising after months of decline.

“The pandemic is not over, and delta changes the calculus,” Joel Wertheim, an associate professor in the Division of Infectious Diseases and Global Public Health at the University of California at San Diego, told The Washington Post.

Further complicating things, federal health officials recently said that data from delta cases suggests that vaccinated people can spread infections — something that did not happen in a significant way with earlier versions of the virus.

The messaging from public health experts and officials is unequivocal: Vaccines are the best protection against severe illness and hospitalization. The vast majority of new hospitalizations from the delta variant are from people who are unvaccinated, making what Rochelle Walensky, director of the Centers for Disease Control and Prevention, calls “a pandemic of the unvaccinated.”

“We continue to see cases, hospitalizations and deaths, increase across the country,” she told reporters at a recent White House briefing. “As we have been saying, by far, those at highest risk remain people who have not yet been vaccinated.”

Public health officials also recommend that vaccinated as well as unvaccinated people should wear masks in indoor public spaces in coronavirus hot spots. Health experts said even though the delta variant is far more infectious than the original strain that took hold in the United States last year, precautions can help everyone limit their risks.

Here’s what to know:

If I’m fully vaccinated, do I need to wear a mask indoors?

If you live or work in communities with high transmission rates, the answer is most likely yes. Amid delta’s rapid spread in late July, the CDC revised its mask guidance for fully vaccinated individuals, advising them to wear masks in public indoor spaces when in areas of “substantial” or “high” transmission. More than 90 percent of U.S. counties met that definition by mid-August.

While indoors in private — say, in a friend or family member’s home — it depends on everyone’s inoculation status and vulnerabilities. If you are around children too young to be vaccinated, for instance, or people who are immunocompromised and therefore unable to mount a full immune response, you would be well-advised to consider wearing one.

That substantially changed the agency’s guidance since mid-May that those who were fully inoculated did not need masks indoors or outdoors in most cases — guidance several health experts who spoke to The Post at the time said was insufficient.

“I think the CDC in May made a mistake,” said Emily Landon, chief infectious-disease epidemiologist at University of Chicago Medicine. “They made a recommendation based on biological science, but not any social science. Unfortunately, the policy of letting people self-sort into vaccinated and unvaccinated resulted in a sort of behavioral science problem.”

Several experts consulted by The Post said it is safe for fully vaccinated people to spend time indoors with others who are fully vaccinated. The shots have proved widely effective, even in crowded indoor settings. But they said it is nonetheless a smart practice to continue wearing masks in environments where there might be people who are not fully inoculated or who might be more vulnerable because of underlying health conditions.

Masks can help prevent the wearer from contracting the coronavirus, and also protect those who haven’t gotten a vaccine and could be at risk of complications if they were to get sick. Though the CDC says that “breakthrough infections” are relatively rare among the fully vaccinated, vaccines are not 100 percent effective and thousands of mostly mild cases have been reported. Experts say it is smart to try to avoid getting even a mild case of the virus.

Is attending a big outdoor gathering such as a wedding or a concert high-risk?

On the spectrum of risk, an outdoor setting for fully vaccinated, masked and socially distanced people is the least risky — but may not be an ideal party situation.

Betty Jean “BJ” Ezell, who serves as a vaccine hesitancy outreach coordinator for Citrus County, Fla., said it’s a good idea to mask up or socially distance if you’re at a large gathering outdoors and don’t know whether the people around you are vaccinated, as “the delta variant has shown that it’s rampant and unforgiving in its ability to spread.”

“When you talk about outdoor weddings and parks, I think physical distancing is still a good thing because an infected person may be asymptomatic,” Ezell said.

While the outdoors is generally less risky for coronavirus transmission because of circulating air, Yonatan Grad, an associate professor at the Department of Immunology and Infectious Diseases at the Harvard T.H. Chan School of Public Health, said to stay aware of your exposure to other people, noting that an outdoor music festival in the Netherlands in early July has since been linked to nearly 1,000 new infections.

Grad encouraged people to look at risk not just through a binary lens of “safe” or “unsafe.” Other factors such as the rates of infection and vaccination in a given area are key. Going to a party in a community with rising covid-19 cases and lackluster inoculation numbers, for example, could be riskier than attending one in an area with high vaccination rates.

“‘Safe’ can imply that you’re totally protected,” he said. “The goal for many people is to be at the lowest risk possible.”

I’ve had only my first dose of the vaccine. Do I have enough protection from the delta variant?

With the two-dose mRNA vaccines, “the data from the U.K. suggest that the protection from a single dose of the vaccine is low for the delta variant,” Grad said. “There’s a big jump in the level of protection with the second dose for the delta variant specifically.”

Wertheim agreed.

“We have this large swath of America that has only gotten one dose, and if we could only get them to get a second shot, I think that’s a group where we could make a big difference,” he said. “If you’ve been slow about getting a second dose, now is the time.”

Wertheim said people should get their second dose even if they’ve had an extended interval since their first shot.

“There’s no evidence to suggest that waiting longer [to get the second dose] is worse,” he said.

My children aren’t old enough to get a vaccine. How can I protect them?

Even though children tend to have milder coronavirus cases, Landon said infections in children are following the same trend lines as adults in delta variant hot spots: States with large outbreaks are seeing more infections in children.

“I understand that it’s really enticing to think of covid as just another cold, but it’s not,” Landon said of virus cases among children. “It’s always best to avoid getting sick at all.”

For children who aren’t old enough to get a vaccine — currently those younger than 12 — Landon said adults and older siblings can help reduce the risk to these younger children by avoiding crowded indoor settings and wearing masks inside.

Extra precautions will be especially important for young children returning to school. The CDC has recommended that those who are eligible get vaccinated to protect those who are not, and urges universal indoor masking for all teachers, staff members and students older than 2, vaccinated or not, in K-12 schools to help prevent the spread of the virus.

In addition to precautionary measures such as mask-wearing, frequent hand-washing and proper respiratory etiquette (covering your nose and mouth when coughing and sneezing), the CDC suggests that schools keep students at least three feet apart in the classroom.

And, of course, those experiencing symptoms should stay home and get tested for the coronavirus.

But covid-19 is not the only concern. Experts also advise common-sense precautions to prevent all respiratory illnesses.

“We still pay attention to hand-washing — sing that ‘Happy Birthday’ song twice — we still pay attention to masking and the fit of the mask,” Ezell said.

However, the intensive surface cleaning that people engaged in early in the pandemic is no longer considered necessary.

Can I resume working out at the gym if I’m vaccinated?

“I wish there were hard numbers we could give for all of these variations to questions about risk,” Grad said. “But it’s a question of what risk you want to tolerate.”

Getting as much ventilation as possible in an indoor setting like a gym, where people may be breathing heavily, is one important way to reduce risk. In addition, you should wear a mask while working out if you live in a high-transmission community.

“If we knew the vaccination status of all the people in the gym, we could have a greater level of comfort,” Grad added. “If we don’t, we might want to be masking — think the same kinds of precautions we have in an airport.”

Landon of the University of Chicago said that because the chance of catching the coronavirus increases with the amount of close contact with infected individuals, even healthy people who are vaccinated run a risk — albeit a low one — when they voluntarily increase their exposure.

“The amount of breathing you do matters — that’s why gyms are kind of risky,” Landon said. “The amount of distance and ventilation reduces your risks, so better if your gym is ventilated and you can get some space between treadmills.”

How do I talk to loved ones who are still hesitant about the vaccine?

Ezell, the vaccine hesitancy outreach coordinator in Florida, said when it comes to speaking with vaccine skeptics, she follows the advice of her pastor: You gain people’s confidence not by “beating them over the head,” but by planting a seed.

Give someone factual information to get them started, Ezell said, and the next person who comes along follows up by “watering,” thereby increasing the number of trusted voices who have shared sound information.

“I think it’s especially important when you’re having these conversations to present with what I call an active listening voice,” Ezell said. “Ask people in particular what their objections are, and don’t interrupt them; let them finish. Then give them the facts in a very calm manner.”

If cases continue to rise with the delta variant, will more restrictions return?

Restrictions such as indoor mask rules are likely to increase. Even before the CDC revised its guidance, Los Angeles County, the nation’s most populous, had become among a growing number of municipalities to reintroduce mask rules.

And as previously mentioned, the CDC said teachers, staff members and students over the age of 2 should be masked in school buildings, regardless of their vaccination status.

Most health experts who spoke to The Post were skeptical that there would be a return to widespread restrictions such as stay-at-home orders and shuttered businesses. Landon and other experts said the reintroduction of restrictions are likely to be hyperlocal and responsive to infection and hospitalization rates in a specific area.

That said, a number of government agencies, health-care organizations and businesses from tech companies to transportation services are requiring employees to get vaccinated or, in some cases, submit to regular testing. Even some restaurants are asking employees — as well as customers — to show proof that they have had the shots.

Landon likened state-imposed measures — such as masking rules — to waging a fight with small children.

“It’s like being exhausted and telling your kids, ‘Fine, you can have ice cream for dinner,‘ ” she said. “You don’t have the will to say ‘no’ anymore.”

She added: “The bottom line, we should have mask mandates indoors. In public buildings, there’s no reason we’re not mandating masks. But will we go back to that? I doubt it. Now I think it will be really hard to go back to those restrictions.”

Ezell agreed there would be resistance.

“The horse has left the barn on relaxing restrictions, so it’s going to be really important that there are perhaps more public service announcements, group meetings, more getting trusted voices involved in communicating information from reliable sources,” she said.

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