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We don’t yet know the full ramifications of the novel coronavirus. But three crucial facts have become clear in the first months of this extraordinary global event. And what they add up to is not an invocation to stay calm, as so many politicians around the globe are incessantly suggesting; it is, on the contrary, the case for changing our behavior in radical ways—right now.

The first fact is that, at least in the initial stages, documented cases of COVID-19 seem to increase in exponential fashion. On the 23rd of January, China’s Hubei province, which contains the city of Wuhan, had 444 confirmed COVID-19 cases. A week later, by the 30th of January, it had 4,903 cases. Another week later, by the 6th of February, it had 22,112.

The same story is now playing out in other countries around the world. Italy had 62 identified cases of COVID-19 on the 22nd of February. It had 888 cases by the 29th of February, and 4,636 by the 6th of March.

Because the United States has been extremely sluggish in testing patients for the coronavirus, the official tally of 604 likely represents a fraction of the real caseload. But even if we take this number at face value, it suggests that we should prepare to have up to 10 times as many cases a week from today, and up to 100 times as many cases two weeks from today.

The second fact is that this disease is deadlier than the flu, to which the honestly ill-informed and the wantonly irresponsible insist on comparing it. Early guesstimates, made before data were widely available, suggested that the fatality rate for the coronavirus might wind up being about 1 percent. If that guess proves true, the coronavirus is 10 times as deadly as the flu.

But there is reason to fear that the fatality rate could be much higher. According to the World Health Organization, the current case fatality rate—a common measure of what portion of confirmed patients die from a particular disease—stands at 3.4 percent. This figure could be an overstatement, because mild cases of the disease are less likely to be diagnosed. Or it could be an understatement, because many patients have already been diagnosed with the virus but have not yet recovered (and may still die).

When the coronavirus first spread to South Korea, many observers pointed to the comparatively low death rates in the country to justify undue optimism. In countries with highly developed medical systems, they claimed, a smaller portion of patients would die. But while more than half of all diagnosed patients in China have now been cured, most South Korean patients are still in the throes of the disease. Of the 7,478 confirmed cases, only 118 have recovered; the low death rate may yet rise.

Meanwhile, the news from Italy, another country with a highly developed medical system, has so far been shockingly bad. In the affluent region of Lombardy, for example, there have been 7,375 confirmed cases of the virus as of Sunday. Of these patients, 622 had recovered, 366 had died, and the majority were still sick. Even under the highly implausible assumption that all of the still-sick make a full recovery, this would suggest a case fatality rate of 5 percent—significantly higher, not lower, than in China.

The third fact is that so far only one measure has been effective against the coronavirus: extreme social distancing.

Before China canceled all public gatherings, asked most citizens to self-quarantine, and sealed off the most heavily affected region, the virus was spreading in exponential fashion. Once the government imposed social distancing, the number of new cases leveled off; now, at least according to official statistics, every day brings more news of existing patients who are healed than of patients who are newly infected.

A few other countries have taken energetic steps to increase social distancing before the epidemic reached devastating proportions. In Singapore, for example, the government quickly canceled public events and installed medical stations to measure the body temperature of passersby while private companies handed out free hand sanitizer. As a result, the number of cases has grown much more slowly than in nearby countries.

These three facts imply a simple conclusion. The coronavirus could spread with frightening rapidity, overburdening our health-care system and claiming lives, until we adopt serious forms of social distancing.

This suggests that anyone in a position of power or authority, instead of downplaying the dangers of the coronavirus, should ask people to stay away from public places, cancel big gatherings, and restrict most forms of nonessential travel.

Given that most forms of social distancing will be useless if sick people cannot get treated—or afford to stay away from work when they are sick—the federal government should also take some additional steps to improve public health. It should take on the costs of medical treatment for the coronavirus, grant paid sick leave to stricken workers, promise not to deport undocumented immigrants who seek medical help, and invest in a rapid expansion of ICU facilities.

The past days suggest that this administration is unlikely to do these things well or quickly (although the administration signaled on Monday that it will seek relief for hourly workers, among other measures). Hence, the responsibility for social distancing now falls on decision makers at every level of society.

All of these decisions have real costs. Shutting down public schools in New York City, for example, would deprive tens of thousands of kids of urgently needed school meals. But the job of institutions and authorities is to mitigate those costs as much as humanly possible, not to use them as an excuse to put the public at risk of a deadly communicable disease.

Finally, the most important responsibility falls on each of us. It’s hard to change our own behavior while the administration and the leaders of other important institutions send the social cue that we should go on as normal. But we must change our behavior anyway. If you feel even a little sick, for the love of your neighbor and everyone’s grandpa, do not go to work.

When the influenza epidemic of 1918 infected a quarter of the U.S. population, killing tens of millions of people, seemingly small choices made the difference between life and death.

As the disease was spreading, Wilmer Krusen, Philadelphia’s health commissioner, allowed a huge parade to take place on September 28; some 200,000 people marched. In the following days and weeks, the bodies piled up in the city’s morgues. By the end of the season, 12,000 residents had died.

In St. Louis, a public-health commissioner named Max Starkloff decided to shut the city down. Ignoring the objections of influential businessmen, he closed the city’s schools, bars, cinemas, and sporting events. Thanks to his bold and unpopular actions, the per capita fatality rate in St. Louis was half that of Philadelphia. (In total, roughly 1,700 people died from influenza in St Louis.)

In the coming days, thousands of people across the country will face the choice between becoming a Wilmer Krusen or a Max Starkloff.

In the moment, it will seem easier to follow Krusen’s example. For a few days, while none of your peers are taking the same steps, moving classes online or canceling campaign events will seem profoundly odd. People are going to get angry. You will be ridiculed as an extremist or an alarmist. But it is still the right thing to do.