What’s at stake in this coronavirus pandemic? How many Americans can become infected? How many might die?

The answers depend on the actions we take — and, crucially, on when we take them. Working with infectious disease epidemiologists, we developed this interactive tool that lets you see what may lie ahead in the United States and how much of a difference it could make if officials act quickly. (The figures are for America, but the lessons are broadly applicable to any country.)













If we stay on the current track, this model predicts that roughly a third of Americans – more than 100 million people — could become infected (including more than nine million at one time). Other estimates are higher, up to two-thirds, but even in this scenario, one million could die. But interventions matter hugely. Ending public gatherings, closing workplaces and some schools, mass testing and fortifying hospitals keep infection rates down and reduce deaths. Here’s that same scenario but shifted so that the interventions begin one month later. The number of infections climbs by more than two million. So it’s not just intervening that’s important — it’s intervening quickly. Yesterday is better than today, which is better than tomorrow. Try it yourself by dragging the intervention bar on the chartslider below to the left or right to change when interventions are put in place. Adjust intervention start date: Aggressiveness matters, too. Adjust the severity of the interventions below to see why: Aggressive measures include widespread testing and ending large gatherings, while mild measures are essentially the status quo (although some places are instituting tougher measures). What matters is not only the total number of infections but also whether many occur at once. Overloaded hospitals and shortages of ventilators in intensive care units would result in people dying unnecessarily from the coronavirus as well as from heart attacks and other ailments. So successful interventions are crucial because they flatten the curve: We are much better off if the 100 million infections occur over 18 months rather than over 18 weeks. Here’s the same number of I.C.U. cases as before, but modeled to occur at a much slower rate.

Any disease model is only as good as the assumptions programmed into it, and there’s so much uncertainty about the coronavirus that we shouldn’t see this model as a precise prediction.

One fundamental unknown is whether warmer weather will help reduce infections, as happens with the seasonal flu. If so, we could see a respite this summer, and then a resumption of cases in the fall (that’s what happened in 1918 with the Spanish flu pandemic). In addition, there are a number of treatments that are being tested and may prove helpful against the coronavirus.

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On the other hand, shortages of protective equipment like masks and chaos in hospitals may lead to higher death rates; the United States also has an older and thus more vulnerable population than China, from which much of the data comes.

“The point of a model like this is not to try to predict the future but to help people understand why we may need to change our behaviors or restrict our movements, and also to give people a sense of the sort of effect these changes can have,” said Ashleigh Tuite, an epidemiologist at the University of Toronto who helped us develop this model. “When we have a new disease introduced in a population, we don’t have the benefit of immunity or vaccines to limit spread, but that doesn’t mean that we can’t control it,” she added. “Other countries have already shown that a strong response can bend the epidemic curve.”

President Trump announced some steps on Wednesday to address the coronavirus, but they focused on the economy and on sharply reducing travel from most of Europe. At this point we may already have tens of thousands of infections in the United States — no one knows, because testing has been catastrophically bungled — and the number of cases is probably doubling every six days or so. In these circumstances, stopping a few new cases from Europe may not matter so much.

Public health specialists say we need a huge expansion of testing, major curbs on public gatherings, suspension of school in affected areas and intensive preparations so that hospitals can still function as infections soar. (We’ve recommended these and other crucial steps here).

David N. Fisman, another University of Toronto epidemiologist who helped us assemble this model, noted that the challenge is that aggressive interventions must be put in place early to be most effective — and yet early in an epidemic the public may not be concerned enough to embrace such measures.

“Early in the epidemic it is very difficult to muster the political will to implement costly, disruptive disease-control policies,” Dr. Fisman said. “What we are hoping to show here is that the calculus is one of short-term pain for long-term gain: Early, aggressive social distancing can substantially reduce the toll of epidemics, which can include the near collapse of health care systems, as we’re currently seeing in Italy.”

We’ll be honest: We worried that the clean lines in the graphics here risk suggesting a false precision. None of us know what lies ahead. But the wise uncertainty of epidemiologists is preferable to the confident bluster of television blowhards. The one thing we can be confident of is that enormous risks lie ahead — including a huge loss of life — if we don’t take aggressive action.

We have already squandered weeks in which the president scoffed at the coronavirus and tried to talk up the stock markets, but it’s not too late: We can still change the course of this epidemic.