From the most respected epidemiologists to public health experts who have navigated past disease panics, from polemicists to political partisans, there are no definitive answers to the central question in American life: As a Drudge Report headline put it recently, “is it ever going to end?”

With children returning to classrooms, in many cases for the first time in 18 months, and as the highly contagious delta variant and spotty vaccination uptake send case numbers and deaths shooting upward, many Americans wonder what exactly has to happen before life can return to something that looks and feels like 2019.

The answers come in a kaleidoscopic cavalcade of scenarios, some suggested with utmost humility, others with mathematical confidence: The pandemic will end because deaths finally drop to about the same level we’re accustomed to seeing from the flu each year. Or it will end when most kids are vaccinated. Or it will end because Americans are finally exhausted by all the restrictions on daily life.

Innumerable predictions over the course of the pandemic have come up lame. Some scientists have sworn off soothsaying. But as they learn more about the coronavirus that bestowed covid-19 on mankind, they build models and make projections and describe the hurdles that remain before people can pull off the masks and go about their lives.

The good news is there is some fuel for optimism.

“I truly, truly think we are in the endgame,” said Monica Gandhi, an infectious-disease specialist and professor of medicine at the University of California at San Francisco. “The cases will start plummeting in mid- to late September and by mid-October, we will be in a manageable place, where the virus is a concern for health professionals, but not really for the general public.”

Gandhi bases her optimism on the fact that all previous epidemics of respiratory viruses have ended through the acquisition of immunity, whether by vaccination or natural infection. Although viruses do keep changing, potentially circumventing people’s defenses, “they mutate quickly, at a cost to themselves,” weakening over time. Gandhi said she believes the delta variant that has hit the United States so hard that this summer will mark the peak of this virus’s strength.

But Gandhi warns she has been wrong before: In February 2020, she said the United States would not tolerate a disease that killed 100 Americans a day; people would come together to do whatever it took to stop that. That didn’t happen.

The bad news is there is too much cause for doubt.

© Marvin Joseph/The Washington Post Students arrive for the first day of school Monday at Eliot-Hine Middle School in Washington.

“We’re in a moment of uncertainty, and humans don’t do well with uncertainty,” said Ezekiel Emanuel, a professor of medical ethics and health policy at the University of Pennsylvania. “Telling people it’s going to be two or three more years of this is really hard, but I don’t think anyone can be comfortable with the current state, with a lot of kids ending up in the hospital and a thousand deaths a day. That’s not returning to normal.”

Emanuel, too, notes that his crystal ball has suffered occasional cloudiness: In March 2020, he said the country would get back to normal around November 2021. For that, his friends dubbed him “Mr. Pessimist.” Now, his message is at least as unwelcome: It’s going to be at least spring 2022 and possibly much longer before most people are ready to resume normal activities, because of the spread of the delta variant, continuing resistance to vaccines and widespread anxiety, especially about children who are not yet eligible to get vaccinated.

Despite the disparities in experts’ opinions, there is a consensus bottom line about the biggest question: Pandemics do end, sort of. (Though there are exceptions, such as malaria.) Only smallpox has been effectively eradicated by human intervention. But many pandemics become endemic, meaning they morph into something that is no longer an emergency, but rather an annoyance, an ugly, even painful fact of life that people simply learn to cope with, like the flu or common cold.

The question is when and how we get to that point.

Some of the nation’s most prominent epidemiologists and public health experts say we are already there — for different reasons.

“The emergency phase of the disease is over,” said Jay Bhattacharya, a professor of medicine and health economist at Stanford University. “Now, we need to work very hard to undo the sense of emergency. We should be treating covid as one of 200 diseases that affect people.”

The pivotal engine driving a return to normal life for Bhattacharya has been the vaccines, “which really do protect against death,” he said. “It’s a miraculous development, and we should just be celebrating it.” By driving down deaths and hospitalizations, especially for the most vulnerable populations — the elderly and people with preexisting health problems — “we have greatly succeeded, and to me, that’s the endpoint of the epidemic because we really can’t do better than that.”

The virus will continue to mutate and there will continue to be outbreaks, both seasonal and in geographic clusters, but “panicking over case numbers is a recipe for continuing unwarranted panic,” he said.

Bhattacharya is ready to resume most pre-pandemic activities. He recently made his first overseas trip, to England, “and it was wonderful,” he said, “even with a mask.”

Gandhi, too, has concluded that as scary and dangerous as the delta variant has been, “we’re sort of at the peak of the pandemic because the delta variant is causing immunity like crazy. Delta comes in like a hurricane, but it leaves a lot of immunity in its wake.”

Although its rapid spread and severe impact on some people are scary, the delta version has a hidden benefit: It makes future variants less likely to be more lethal, Gandhi said.

Covid isn’t going away — “we’re going to get it,” Gandhi said — but as immunity increases, the virus will cause less harm. People will come to terms with it as they have with the common cold or the flu.

“Unless you just sit in your room, you’re going to get it in your nose,” she said, “but at least in this country, it will be manageable.”

The big problem now, Gandhi said, is fear, “excessive fear of the pandemic on both sides,” she said. “Democrats overestimate the death rate and Republicans underestimate it.”

© Cedar Attanasio/AP Demonstrators protest coronavirus vaccinations and mask mandates Aug. 20 in Santa Fe.

That produces the psychological and political hurdles that are preventing a return to normal life, she said. Recent polling indicates most Americans’ perception of the pandemic has shifted markedly this summer, as the delta variant swept away the optimism of springtime. In NBC News polls in April and August, the percentage of Americans saying that the worst of the coronavirus is behind us collapsed from 61 percent to 37 percent.

Gandhi said the trouble lies with some Democrats resisting resuming activities they take part in during flu season without hesitation and some Republicans refusing to take the vaccine or wear masks in crowded indoor spaces.

“I live in the bluest city in one of the bluest states, and I see this profound fear of the virus leading to extraordinary acceptance of lockdowns and keeping schools closed,” she said. But Gandhi says those hesitations can melt away quickly as case numbers fall.

Julie Swann views Gandhi as overly optimistic about how and when normal life might return. “She’s wrong,” said Swann, a systems engineer at North Carolina State University who advised the Centers for Disease Control and Prevention on the H1N1 pandemic. “And I hope it takes longer than she’s saying because that will be much safer.”

© Eamon Queeney for The Washington Post Julie Swann, a systems engineer, advised the Centers for Disease Control and Prevention on the H1N1 pandemic.

Swann said Gandhi’s argument that the delta variant will create so much immunity that life can return to normal “is a really apocalyptic way of getting there. Do you want delta to burn through the population, creating immunity at a very high cost, or would you rather just wear a mask?”

The key factor for Swann as she creates models projecting how the virus is likely to play out is the role children play in spreading the disease. The path to normal life is through getting children vaccinated, she said, and that is not likely to happen in large numbers until early next year.

“Children transmit viruses to each other, to their families, to their communities,” Swann said. “The first step toward normalcy is getting children vaccinated, at least for ages 5 and up. Right now, unfortunately, what we’re seeing in Florida is many, many children getting infected.”

Swann sees several possible routes back to normal life, including letting the virus burn through the population, focusing on masking and hybrid schooling, or a return to lockdowns. But her preferred pathway is mass vaccination of children — which can only happen after the vaccines are approved for the 5-to-11 age group, a step that’s not expected until at least later this year — along with masking and increased testing.

Ten years from now, the coronavirus “will be like influenza — it can cause death, but nothing like what we see now,” Swann said. But in the next year or so, the best Americans can hope for is a partial return to normalcy, with hospitals no longer being crushed with covid patients and occasional surges of covid in communities with low vaccination rates.

“We are not New Zealand,” she said. “We neither have the will nor the ability to control every case coming into our country. But if we can vaccinate most kids, we will get to a point where we no longer need masks in schools, and we’ll have a return to normalcy, though it will look different in different places.”

For now, Swann has started traveling again domestically, though she can’t imagine taking a foreign trip or going to a party until after her child has been vaccinated, probably around next February. “That changes the whole ballgame,” she said.

The wild card, as it has been for adults, is how quickly and widely children are vaccinated.

And the national divide over vaccines, masks and other such politicized public health measures could well end up being the reason the pandemic persists in the United States, said Alex Berenson, a novelist and former New York Times reporter. Berenson’s agitation against the vaccine has become a popular source of succor for many who have refused to get the shot, but it also got him permanently banned from Twitter for what the company called “repeated violations of our COVID-19 misinformation rules.”

“I don’t know how we get there politically,” Berenson said of the quest for an endgame. “We are at a very confused moment.”

He said his readers “are long done with covid. And personally, I have not worn a mask for months, and no one has challenged me anywhere about whether I am vaccinated or not.” (He’s not.)

But “obviously some large number of Americans feel differently,” he said. “They are happy to live under government strictures indefinitely. . . . These two populations cannot comfortably exist. This is not a medical problem. . . . This is a political and social problem and it will have to be resolved politically, I suppose.”

Berenson said he believes Americans can return to normal life right now, without mask mandates, contact tracing or vaccine passports. But “can” and “will” are different, and he expects it might be late 2023 or later — perhaps after the next presidential election — before any consensus might develop about returning to normal life.

Any consensus on ratcheting down the fear and anxiety that the virus has spawned is more likely to emerge from public health campaigns than political campaigns, said Bhattacharya, the Stanford professor. It’s up to public health officials to persuade Americans that if they are vaccinated, they can return to many pre-pandemic activities, he said.

Bhattacharya, for example, is looking forward to teaching in person this fall and said he will happily meet with students, as Stanford is requiring vaccinations for everyone on campus.

© Hector Vivas/Getty Images Cleaning staff at Motolinia University in Mexico City on Aug. 30.

In contrast, as Emanuel returns to teach at Penn, “I’m nervous,” even with vaccination and mask mandates, he said. “I’ll be testing myself and students will be tested, and I’m bringing a HEPA [air] filter into the classroom, and I’m still a little nervous about long covid. We’re still unclear on the direction of this thing. It’s plausible that we’ve hit the peak, but it’s also plausible that other mutations will be even more efficient.”

Emanuel will know it’s time to resume normal behavior “when this thing looks like a flu, when the health-care system is operating normally, when my friends aren’t constantly asking me, ‘What can I do to stay safe?’ ”

That time will come only after there’s more data about how and when people get long covid, about what happens when people mix different vaccines, about the pace and character of the virus’s mutations.

“People are pretty burned out 18 months into this thing,” Emanuel said. “And the exhaustion has been made worse by the rapid seesaw we’re having — take your masks off, put them back on. It’s all very confusing, but we have to be honest: We don’t know when, we don’t know how. We don’t know.”