Three months ago, no one knew that SARS-CoV-2 existed. Now the virus has spread to almost every country, infecting at least 446,000 people whom we know about, and many more whom we do not. It has crashed economies and broken health-care systems, filled hospitals and emptied public spaces. It has separated people from their workplaces and their friends. It has disrupted modern society on a scale that most living people have never witnessed. Soon, most everyone in the United States will know someone who has been infected. Like World War II or the 9/11 attacks, this pandemic has already imprinted itself upon the nation’s psyche.

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A global pandemic of this scale was inevitable. In recent years, hundreds of health experts have written books, white papers, and op-eds warning of the possibility. Bill Gates has been telling anyone who would listen, including the 18 million viewers of his TED Talk. In 2018, I wrote a story for The Atlantic arguing that America was not ready for the pandemic that would eventually come. In October, the Johns Hopkins Center for Health Security war-gamed what might happen if a new coronavirus swept the globe. And then one did. Hypotheticals became reality. “What if?” became “Now what?”

Updated at 10:06 a.m. ET on April 3, 2020.

As the coronavirus pandemic continues, many people are now overthinking things they never used to think about at all. Can you go outside? What if you’re walking downwind of another person? What if you’re stuck waiting at a crosswalk and someone is there? What if you’re going for a run, and another runner is heading toward you, and the sidewalk is narrow? Suddenly, daily mundanities seem to demand strategy.

Much of this confusion stems from the shifting conversation around the pandemic. Thus far, the official line has been that the new coronavirus, SARS-CoV-2, could be transmitted only through close contact with infected people or contaminated surfaces. But recently, news reports have suggested that the coronavirus can spread through the air. After 60 choir members in Washington State rehearsed together, 45 fell sick, even though no one seemed symptomatic at the time. Now people who were already feeling cooped up are worrying about going outside. Many state guidelines are ambiguous, and medical advice can muddy matters further. When the writer Deborah Copaken came down with COVID-19 symptoms, her doctor chided her for riding her bike through New York City a week earlier. Going outside in the city wasn’t safe, the physician implied, with “viral load everywhere.”

Get your battle rhythm, I keep telling myself, as I put on my oversize sweatpants for the third day in a row. Staying inside, away from our offices, routines, and community, feels jarring even for those who, on a rational level, understand the need for extreme social distancing. The good side is having more family time. But everything seems upended, even to homeland-security professionals who argued for upending everything to slow the spread of COVID-19.

Just as seasickness abates once you can see the shore, the disruptions that the country is now experiencing would be easier to manage if we knew they would end soon. The community-isolation effort happened remarkably fast—within days, whole communities all but closed down, and earlier this week the federal government finally recommended the same. On Thursday, Governor Gavin Newsom ordered the entire state of California to stay home “until further notice.” But the way the crisis ends will be far more muddled. There isn’t going to be one all-clear signal—and certainly not one anytime soon.

From inside her living room in London, Paula Koelemeijer can feel the world around her growing quieter.

Koelemeijer, a seismologist, has a miniature seismometer sitting on a concrete slab at the base of her first-floor fireplace. The apparatus, though smaller than a box of tissues, can sense all kinds of movement, from the rattle of trains on the tracks near Koelemeijer’s home to the waves of earthquakes rolling in from afar. Since the United Kingdom announced stricter social-distancing rules last month, telling residents not to leave their home except for essential reasons, the seismometer has registered a sharp decrease in the vibrations produced by human activity.

With fewer trains, buses, and people pounding the pavement, the usual hum of public life has vanished, and so has its dependable rhythms: Before the spread of COVID-19 shut down the city, Koelemeijer could plot the seismometer’s data and see the train schedule reflected in the spikes, down to the minute. Now, with fewer trains running, the spikes seem to come at random.

In a matter of weeks, the coronavirus has gone from a novel, distant threat to an enemy besieging cities and towns across the world. The burden of COVID-19 and the economic upheaval wrought by the measures to contain it feel epochal. Humanity now has a common foe, and we will grow increasingly familiar with its face.

Yet plenty of this virus’s aspects remain unknown. The developing wisdom—earned the hard way in Wuhan, Washington, and Italy—has been that older people and sicker people are substantially more likely to suffer severe illness or die from COVID-19 than their younger, healthier counterparts. Older people are much more likely than young people to have lung disease, kidney disease, hypertension, or heart disease, and those conditions are more likely to transform a coronavirus infection into something nastier. But what happens when these assumptions don’t hold up, and the young people battling the pandemic share the same risks?

In the emergency-department waiting room, 150 people worry about a fever. Some just want a test, others badly need medical treatment. Those not at the brink of death have to wait six, eight, 10 hours before they can see a doctor. Those admitted to the hospital might wait a full day for a bed.

I am an emergency-medicine doctor who practices in both Manhattan and Queens; at the moment, I’m in Queens. Normally, I love coming to work here, even though in the best of times, my co-residents and I take care of one of New York City’s most vulnerable, underinsured patient populations. Many have underlying illnesses and a language barrier, and lack primary care.

For Donald Trump’s reelection campaign, many numbers matter: the number of Americans who get sick and perish from the coronavirus. The number of months before the economy begins to reopen and rebound. The number of Americans who lose their health insurance and home after losing their job. For political scientists, one number is of particular interest, and it currently stands at –18.3.

That is an estimate of how fast the economy is collapsing in the second quarter, an annualized rate derived by Mark Zandi of Moody’s Analytics. It is a measure of how much less the American economy is producing as businesses close and joblessness swells and the pandemic kills. And it is one of the strongest predictors of whether an incumbent is likely to win reelection: An additional percentage point of GDP growth translates roughly into an additional percentage point of the vote share. Americans are seeing their economy evaporate at the fastest pace in modern history, and that foretells a Democratic landslide in the fall.

Updated at 4:40 ET on March 30, 2020.

The new coronavirus has brought American life to a near standstill, closing businesses, canceling large gatherings, and keeping people at home. All of those people must surely be wondering: When will things return to normal?

The answer is simple, if not exactly satisfying: when enough of the population—possibly 60 or 80 percent of people—is resistant to COVID-19 to stifle the disease’s spread from person to person. That is the end goal, although no one knows exactly how long it will take to get there.

There are two realistic paths to achieving this “population-level immunity.” One is the development of a vaccine. The other is for the disease to work its way through the population, surely killing many, but also leaving many others—those who contract the disease and then recover—immune. “They’re just Teflon at that point,” meaning they can’t get infected again and they won’t pass on the disease, explains Andrew Noymer, a public-health professor at UC Irvine. Once enough people reach Teflon status—though we don’t yet know if recovering from the disease confers any immunity at all, let alone lifelong immunity—normalcy will be restored. (It may also turn out to be the case that people who are immune to the disease can still pass it on under certain circumstances.)*

The Trump administration has just released the model for the trajectory of the COVID-19 pandemic in America. We can expect a lot of back-and-forth about whether its mortality estimates are too high or low. And its wide range of possible outcomes is certainly confusing: What’s the right number? The answer is both difficult and simple. Here’s the difficult part: There is no right answer. But here’s the simple part: Right answers are not what epidemiological models are for.

Epidemiologists routinely turn to models to predict the progression of an infectious disease. Fighting public suspicion of these models is as old as modern epidemiology, which traces its origins back to John Snow’s famous cholera maps in 1854. Those maps proved, for the first time, that London’s terrible affliction was spreading through crystal-clear fresh water that came out of pumps, not the city’s foul-smelling air. Many people didn’t believe Snow, because they lived in a world without a clear understanding of germ theory and only the most rudimentary microscopes.

Viktor Orbán is the prime minister of Hungary. He has been in power since 2010. During that time, he has underinvested in hospitals. Instead, public money has gone to pet projects, many of them related to the sports he enjoys. In his home village, Felcsút, the government built an elaborate soccer stadium with a heated field and 3,814 seats—which, as The New York Times noted, is twice the number of people who live in the village. Meanwhile, the nearby county hospital’s emergency ward has long struggled to cope with even an ordinary number of patients. On one evening in October, a visiting Times reporter found two harried doctors on call at midnight, and 30 people waiting for treatment.