Our collective fatigue appears in sunken faces. In reddened eyelids, slumped shoulders and forlorn stares. It appears on street corners, in dark taverns, between dusty upturned chairs; and on hospital intercoms, in despondent voices, in between sobs. It’s a product of worry, and sickness, and loss, and stress. Entering Month 10 of the COVID-19 pandemic, it appears just about everywhere in the United States — and perhaps most of all inside the heroes trying to end it.

Yahoo Sports consulted dozens of them over the past month. Top public health officials, epidemiologists, psychologists and more. Our goal was to map out America’s path forward, past the plague, toward normalcy. And that’s precisely what this story will do.

But interviews began with wellness checks: How’s everything going?

“It's not going great,” one doctor shot back reflexively. “It's just one of these terrible, terrible — I'm so [expletive] overbooked, it's ridiculous.”

Sometimes I’d ask specifically: Are you holding up OK, mentally?

“I have no choice,” Anthony Fauci responded.

“Um, it's been a difficult eight months,” Philadelphia public health commissioner Tom Farley said.

Two hundred and seventy-four days into the pandemic, millions of Americans are not holding up OK. Officials nationwide reported more than 3,000 COVID-19-related deaths on Wednesday, a record high. Hospitals are once again overflowing. Lives, in countless ways, are still disrupted. And some experts believe the worst is yet to come. Which is why many, in recent weeks, declined opportunities to talk about 2021. The present, a few implied, is too dire. The future, some said, is too uncertain, with too many overlapping unknowns.

But many also recognize the value of hope. And hope, for the first time in ages, is percolating. Yes, the virus is still raging. Yes, this may only be the chronological halfway point of the pandemic. But the second half looks rosier than the first. On Thursday, an FDA panel voted to authorize the first of several vaccines. And the end, finally, came into focus.

“It's still a long tunnel,” says Bill Schaffner, an infectious disease specialist at Vanderbilt. “But there is a big light now at the end of the tunnel.”

When will the pandemic end?

Any day now, the Boeing Dreamliners will rise. Semis will rumble along interstates. Planes and trucks will carry thousands of high-tech glass vials from a giant pharmaceutical plant in western Michigan to hundreds of locations coast to coast. Soon, if all goes to plan, citizens will roll up their sleeves. Doctors will inject the vaccine into arms. And they’ll initiate the beginning of the end.

The vaccine, to be clear, won’t change a single American life in 2020. Each injection will require a second three weeks later. Each vaccinated person then must wait a week or two more for immunity to kick in. And even then, whether immunization will serve as a personalized ticket to normalcy is a vexing question. Public health officials grappled with it as we spoke.

Those first doses, however, will kickstart the grandest and most urgent vaccination campaign in human history. And it should allow us to conquer the pandemic. The question is how, and how soon, the war will end.

There is no unanimously defined endpoint. No day in which Americans will flood downtown streets, rip off their masks and roar. The virus, experts clarify, won’t just disappear. Each of us will experience the climax differently. And some, in fact, have long since opted out of the war. Millions are already proceeding with life as normal. Some don’t believe COVID-19 exists.

But there is a widely agreed-upon societal goal. What we are striving for, public health officials explain, is a point at which widespread normal behavior will no longer spur uncontrolled coronavirus spread. A point at which our personal risks no longer endanger society at large. It’s what Chicago public health commissioner Allison Arwady calls the “epidemiological end” or “functional end.” That’s when officials will allow sports stadiums to fill, and traditional gatherings to resume, and nightlife to flourish. That’s when we’ll have won the war.

And we win the war by achieving herd immunity.

Herd immunity

On the last weekend before the world froze, before any of us knew how bad it would get, I went out for pizza with three friends. Glasses clinked. A wood-fired oven blazed. Outside, traffic roared. Perhaps you have similar memories — of one last Friday happy hour with a coworker; of one last face-to-face meeting with your boss; of one last adventurous evening with your spouse.

This is the normalcy we crave. And it isn’t possible right now, because if you’d had COVID-19 that Friday, you’d have infected all three of your companions. And the boss might infect five other employees; the co-worker might infect her parents; the spouse might infect two friends. One case becomes three more, and three become nine, and perhaps none of those 13 people gets seriously sick. But before long, 59,000 is becoming 177,000, which becomes 531,000, which becomes 1.6 million. Communities get ravaged. Hospitals weep. Thousands die.

To interrupt those chains of devastation, billions of humans overhauled their lives. Behavioral adjustments became our chief battle tactic. But behavioral adjustments don’t achieve herd immunity alone. Their purpose was to stall, as we searched for a weapon that could. And now we have it. The vaccine, Fauci says, will be “an extraordinary addition to our armamentarium of safety measures.” And when used at scale, it will make those behavioral adjustments less necessary.

Imagine a world of Average Joes who behave like you and me — who if infected would spread the virus to three people each. But now imagine 80% of them are immunized. Now, one Joe infects 0.6 others, not three. Now, 59,000 cases become 35,400, which become 21,240 and then 12,744. The virus, if it cannot find hosts to live in, dies a slow death. This is herd immunity, and most experts believe we’ll reach it via vaccination in the summer or fall of 2021. “I think we're gonna get there faster than expected,” says Eric Topol, executive vice president at Scripps Research. Local and federal officials exude cautious optimism as well.

The problem is that we won’t know when we arrive. Because not even the most brilliant biostatisticians on the planet know what the herd immunity threshold is. There is some percentage of the population that must be immunized to get there. It includes the estimated 20-25% of Americans who have already developed immunity through infection. Some experts say the target could be under 50%. Others, including Fauci, believe it’s upward of 75%. Most models think it’s somewhere in between.

The only correct answer is that we, the humans hoping to reach it, can change it.

The threshold rises and falls with the virus’ basic reproductive rate — the number of people to whom the average person spreads COVID-19 when behavior is normal and nobody is immune. In the scenarios above, that rate was 3. In reality, it’s neither fixed nor known. In some communities, it could be higher than 5. In others, it could be below 2.

“Different places will support a different reproductive number,” says Jeffrey Shaman, an infectious disease forecaster at Columbia. “And that's because a place like Manhattan — where in its natural state I run into thousands of people everyday, passing them on the streets, getting on subways, at workplaces, restaurants and such — is very different in terms of the opportunities it presents to spread a virus compared to some rural county in eastern Montana.” Manhattan’s herd immunity threshold, therefore, will be higher.

But Manhattan’s citizens can also lower it — temporarily, to avoid sickness and death before vaccines arrive, and perhaps permanently too. The basic reproductive rate is a function of normal behavior. A new interpretation of “normal” would make the threshold more reachable. Slight behavioral changes — more telecommuting, physical distancing when not inconvenient — could hasten our march toward herd immunity.

So could technology that tells us, immediately and often, whether behavioral changes are necessary.

The non-vaccine catalyst

When you woke up this morning, and squirmed out of bed, and peeked out your window, and prepared to confront your day, you likely didn’t know whether you had COVID-19.

Perhaps you didn’t consciously think about it. But that uncertainty has informed the past nine months of your life. You haven’t known, for sure, whether you should self-isolate or live carefree. So you’ve split the difference. You’ve seen friends, but only occasionally, and always outdoors. You’ve gone into work, but only when necessary.

But what if you could know? What if, when you awake in March to chirping birds and radiant sunlight, and steel yourself for Year 2, you could confidently choose between freedom and extreme caution?

Those are versions of the question Michael Mina, an epidemiologist at Harvard, has been asking since the spring. And he’s settled on this answer: If half of America, even just twice a week, could know with near certainty whether they were COVID-positive or not, “we would get this virus well under control within a month."

We could do that, he explains, with low-cost, rapid-result antigen tests.

Some 10 million-20 million per day, used strategically, could “remove the virus from most communities, or greatly suppress it, without the need for a vaccine," Mina says. Mathematical models, and now real-world examples, are his evidence. The government could approve and distribute cheap, specialized paper strips. You’d swab your own nose every fourth morning, or before an outing. You’d slide the swab into a small tube, and slide the paper strip in alongside it, and learn about your COVID contagiousness within minutes. The result would clear you to socialize — or tell you to stay home and avoid spreading disease.

The U.S. government, thus far, has been reluctant to push these tests. But Mina and others are hopeful that will change. Fauci has warmed to them. “Frequent, rapid, point-of-care-type tests that are given repetitively has a very important place in how we address this outbreak,” he told Yahoo News last month. Mina believes there is “building support in the president-elect's administration” as well. “It's one of his top priorities, to get rapid testing out to the people,” Mina said of Joe Biden last month.

The rapid tests would curb asymptomatic spread. They’d help unshackle restaurants, and perhaps even NBA arenas. They’d allow us to make more informed behavioral adjustments, which would lower the virus’ reproductive rate, which would lower the bar for herd immunity. Like masking and distancing, they’d be a catalyst.

But they wouldn’t replace vaccines, nor vice versa. They’d work in concert. Like masking and distancing, they’d probably be recommended regardless of vaccination status. Because the vaccines, experts say, might not be quite as powerful as you assume.

The ‘doomsday scenario’

The very first vaccine doses will go to healthcare workers. Nursing-home residents and staffers are next in line. Then the elderly, and essential workers, and others at high risk of severe disease. Who, exactly, will qualify as “essential”? Which underlying conditions make somebody “high-risk”? Those decisions are in the hands of states.

But the principles they’ll all use are similar. The priority is direct protection of the vulnerable. And direct protection is what we know these vaccines will provide. Pfizer’s and Moderna’s, both of which should be approved this month, prevent disease with over 90% efficacy. As those priority groups, which total more than 100 million people, become immune throughout winter, hospitalization and death rates should decline. Cases should too. With an estimated 50 million or 60 million Americans having already been infected by COVID-19, around half of U.S. adults could be immune to the disease by spring.

Reaching herd immunity, however, will hinge on another critical question: Do the vaccines block infection? Or merely the symptoms and severe outcomes that stem from it? Could millions who’ve been vaccinated still catch the virus, carry it asymptomatically, and spread it?

Experts aren’t sure. Trials weren’t designed to answer that question. It’s arguably the biggest of 2021. And theories vary. Vaccination could offer near-complete protection. Or it could protect the lungs but not the nose, and could therefore prevent disease but not transmission. That’s what John Moore, a virologist at Cornell, calls the “doomsday scenario.” In it, the vaccines are still tremendously useful. But downstream, deviations from the ideal scenario are stark.

Ideally, vaccination also provides indirect protection, even to the unvaccinated. If 60% of a population is fully immune, the other 40% are 60% less likely to contract COVID-19. But in the doomsday scenario, indirect protection doesn’t exist. The 40% are just as likely, if not more likely, to get sick. Because 100% of the population can still spread the disease.

Moore, to be clear, thinks this doomsday scenario is “unlikely.” A few other experts interviewed for this story agreed. But most felt uncomfortable speculating. Some think it’s entirely realistic. The most likely scenario is somewhere in between the two extremes. “Even if [the vaccine] doesn't prevent asymptomatic infection,” says Paul Offit, director of the University of Pennsylvania’s Vaccine Education Center, “it may still prevent a critical amount of shedding, which would make the person significantly less contagious.” The reality, for now, is that we simply don’t know how contagious the average vaccinated person will be.

Which is why public officials are likely to recommend continued mask-wearing, even as we get antsy in the spring. Vaccination might push case counts downward. But Americans eager to resume lives will push back. The march toward herd immunity will depend on the vaccines’ ability to curb contagiousness, which we can’t control; but also on our behavior, which we very much can control; and on another massive unknown: how many Americans will want to get vaccinated.

The inflection point

For the first few months, the primary constraint on vaccination will be supply. Millions of doses have already been produced. But hundreds of millions are needed, and distribution, in the words of a former HHS secretary, is a “logistical nightmare.” It will involve the military, Congress and several federal agencies; governors, local health departments and healthcare facilities; FedEx, United Airlines and ultra-cold freezers; pharmaceutical giants, manufacturing companies and CVS.

If all those entities and dozens more harmonize flawlessly, 100 million Americans could be vaccinated by the end of February. That’s according to Moncef Slaoui, head of Operation Warp Speed, the federal government’s multi-pronged vaccine initiative. And “by the middle of 2021,” Slaoui has said, “we would be able to have vaccinated the U.S. population.” Fauci also gives a summer timeline. Most experts expect hiccups and moderate delays. Funding is already an issue. But production will accelerate. More vaccines will join the arsenal. Several could be available to the general public in the spring. Citizens will flock to pharmacies, physicians’ offices and pop-up clinics. You’ll receive your shot — for free — plus reminders to return for a second. Day by day, dose by dose, the country will become increasingly immune.

And then, at some stage, it will reach an inflection point.

At some stage, supply will meet demand. Soon thereafter, the challenge will flip, from production to outreach. Rural counties and neglected neighborhoods can be hard to reach. More importantly, vaccine hesitancy exists nationwide. It’s fueled in some cases by misinformation and conspiracy theorists; and in others by a fact-based mistrust of government healthcare.

Public officials know this, and will work to foster trust. They’ll present their science. They’ll explain that there is no evidence that COVID-19 vaccines are unsafe, and substantial evidence that they are effective. They’ll also turn to “opinion leaders,” such as celebrities or athletes, who can influence public thought; and to community leaders, such as ministers, who can influence followers. The past three U.S. presidents have even volunteered to get vaccinated on camera. The campaigns to ease skepticism will be both grassroots and digital, local and national, hyper-focused and expansive.

Yet some folks will remain skeptical. Nobody expects vaccine uptake to reach 95%. A September survey suggested only 51% of Americans would “probably” or “definitely” get vaccinated. Subsequent polls have shown that number rising, most recently to 63%. Public health officials expect the ascent to continue as safety data becomes widely available and studies broaden. Mandates could also inflate uptake. The New York Times recently reported that Biden’s transition team was discussing them. At the very least, some employers could make vaccination a prerequisite for jobs.

Still, though, acceptance will be patchy. More broadly, the pandemic’s final stages will be “geographically heterogeneous,” Topol explains. Vaccination rates will vary from region to region, from town to town, from neighborhood to neighborhood. Behavior, and therefore herd immunity thresholds, will vary too. The communities who stay vigilant, and adapt lives to lower their herd threshold, and widely accept vaccines to meet it, will win the race to normalcy — perhaps by June or July. The ones who ditch masks in April, and sprint too eagerly in May, and widely refuse the vaccine, will stagger to the finish.

The future

The final laps will be slow. The tail, says Farley, the Philadelphia official, will be “very long.” Summer might feel normal. Offices will open. Beaches will brim. Basketball courts will bustle. And your life might be 95% of what it used to be. COVID risk will feel low. Behavior “will just simply bounce back,” says Steven Taylor, author of The Psychology of Pandemics. “People will be astonished.”

The last 5% of normalcy, however, will be the most difficult to recapture. Because we won’t know when we’ve passed the point of no return. Herd immunity is invisible, so many cities and states will advance cautiously. “Instead of using a light switch, more of a dimmer switch,” Arwady, the Chicago health chief, says. They’ll partially lift one set of restrictions, then sit tight. For weeks, they’ll monitor data and assess impact. If cases stay flat or in decline, they’ll ease up some more. The riskiest venues — the “stadiums and theaters and restaurants,” Fauci says — will expand from 25% capacity to 50%, for example. Then perhaps to 75%. But in some locales, the virus might resurge. Some governments might respond by backpedaling.

Others, though, will stomach small spikes and forge ahead. Even if cases rise, they shouldn’t rise uncontrollably come summer. Therapeutics and immunization should keep a growing number of ICU beds vacant. It is at this point, with a widely available vaccine, that anybody who refuses it — who chooses to leave themselves unprotected against COVID-19 — could be considered personally responsible for any consequences. It’s at this point that their sickness will no longer overwhelm healthcare systems. It’s at this point that the pandemic will end.

The virus, experts say, will remain with us for years, if not decades. It will pop up here and there, perhaps more often in winter, perhaps primarily among children. But when it does, contact tracers will speed to the scene. Right now, they are mired in a futile game of whack-a-mole against 200,000 unseeable opponents. With cases low, and outbreaks localized, containment can succeed.

The pandemic’s toll, in so many ways, will be irreversible and terrifyingly steep. Trillions of dollars. Hundreds of thousands of human lives. Millions more forever harmed. Countless Americans have lost loved ones or careers in 2020. Some who’ve battled COVID will struggle physically throughout 2021 and beyond. And for some, Taylor says, the trauma of 2020 will leave lasting psychological damage.

But for most, he predicts, life will go on. Perhaps, in August or September, you’ll venture to your first concert in three years. Perhaps the following week, your first baseball game in two. You’ll meet buddies at a nearby bar. Then you’ll wade through a buzzing concourse to your ballpark seat. You’ll gaze around, and find joy in the sold-out crowd, in the sheer volume of humanity. You’ll laugh at the drunk fan five rows back as he spews obscenities. You won’t be afraid that he might be spewing a virus too.

And perhaps that same night, your parents will go out for dinner and a play. Perhaps the following night, you’ll join them and their parents for a full-family gathering. A week later, you won’t feel the need to check in on their well-being. Two weeks later, your local public health department will scrutinize case counts and positivity rates and hospitalizations. Doctors won’t see anything troubling. And they’ll exhale.

“When that happens,” Fauci says, “then we're back to normal.”