WASHINGTON — The top government scientists battling the coronavirus estimated on Tuesday that the deadly pathogen could kill 100,000 to 240,000 Americans as it ravages the country despite social distancing measures that have closed schools, banned large gatherings, limited travel and forced people to stay in their homes.
Dr. Anthony S. Fauci, the nation’s leading infectious disease expert, and Dr. Deborah L. Birx, who is coordinating the coronavirus response, displayed that grim projection at a White House briefing, calling it “our real number” but pledging to do everything possible to reduce it.
As dire as those predictions are, Dr. Fauci and Dr. Birx said the number of deaths could be much higher if Americans did not follow the strict guidelines vital to keeping the virus from spreading. The White House models they displayed showed that more than 2.2 million people could have died in the United States if nothing were done to try to stop the spread of the virus.
Those conclusions were based on a continuing analysis of cases in the United States and generally matched those from similar models created by public health researchers around the globe. The two public health officials urged people to take the restrictions seriously, and a subdued President Trump, appearing with them, echoed that message, saying that now is not the time to relax.
“I want every American to be prepared for the hard days that lie ahead,” Mr. Trump said, predicting that there will “light at the end of the tunnel” in the future but warning, “We’re going to go through a very tough two weeks.”
Dr. Fauci and Dr. Birx showed charts indicating that coronavirus cases in New York and New Jersey have risen far higher than in other parts of the country, a fact that they said gives them hope that the overall number of deaths might be lower if people in the rest of the states follow the guidelines for at least the next month.
But outbreaks in New Orleans, Detroit and other cities are growing quickly, and experts say it is unclear whether social distancing measures can stop them from rising even more in the next few weeks. Recent estimates in Florida suggest that it may be entering a phase of exponential growth.
Dr. Fauci, the director of the National Institute of Allergy and Infectious Diseases, stressed that even with those efforts, it is possible that nearly a quarter-million people in the United States could lose their lives.
“As sobering a number as that is, we should be prepared for it,” he said.
Mr. Trump, who on Sunday extended for 30 days the government’s recommendations for slowing the spread of the virus, made it clear that the data compiled by Dr. Fauci and Dr. Birx convinced him that the death toll would be even higher if the restrictions on work, school, travel and social life were not taken seriously by all Americans.
Mr. Trump said the virus was a “great national trial unlike any we have ever faced before,” and said it would require the “full absolute measure of our collective strength, love and devotion” in order to minimize the number of people infected.
“It’s a matter of life and death, frankly,” he said, offering a sober assessment of the pandemic’s effect on the United States. “It’s a matter of life and death.”
As of Tuesday, more than 183,500 cases of the virus have been reported in the United States, with more than 3,700 deaths — more than 1,500 of which are in New York, the center of the nation’s outbreak.
Gov. Andrew M. Cuomo, Democrat of New York, told residents of the state on Tuesday that things would continue to get worse — the peak was not expected in the state for another one to three weeks.
On Wall Street, the S&P 500 declined 1.6 percent on Tuesday, the end of a month in which the index fell 12.5 percent.
The projection released on Tuesday was the first time that Mr. Trump’s administration has officially estimated the breadth of the threat to human life from the disease caused by the coronavirus, Covid-19. In the past several weeks, Dr. Birx and Dr. Fauci have resisted predicting how many people might die in the pandemic, saying that there was not enough reliable data.
That is no longer the case, they said.
Public health scientists spent the past week constructing a model that could predict how widely the virus would spread in the coming months and how many people who get infected would succumb to the disease. Dr. Birx said the result was clear: The only way to minimize deaths is to continue the difficult restrictions on American life.
“There’s no magic bullet. There’s no magic vaccine or therapy. It’s just behaviors,” Dr. Birx said. “Each of our behaviors, translating into something that changes the course of this viral pandemic over the next 30 days.”
The new government estimates came to the same conclusion that other researchers have: that even with the isolation efforts already underway to limit the spread of the virus, infections are almost certain to soar, straining the ability of hospitals to care for infected patients and leading to a growing number of deaths.
One of those models, created by scientists at the University of Washington’s Institute for Health Metrics and Evaluation, predicts that deaths from the virus in the United States will rise rapidly during the month of April, from about 4,000 to almost 60,000, even with the many restrictions on movement now in place. The study suggests that the pace of deaths will eventually slow down, reaching a total of about 84,000 by the beginning of August.
The model assumes that social distancing measures will be broadly effective across the country and uses the severe lockdown in Wuhan, China, to calibrate how the outbreak might play out in the United States.
That approach has some critics because control measures imposed in the United States have generally been less stringent than those in Wuhan. While officials have told more than 250 million people to stay at home, some parts of the country, especially in the South, have resisted or delayed similar measures for fear of the economic consequences.
“Their model gives us the range of possible outcomes if we manage to successfully slow the spread of disease,” said Carl T. Bergstrom, a professor of biology at the University of Washington. “If we fail at those measures, we face outcomes far worse than any included in the range of possibilities predicted by their model.”
A second study, released on March 17 by the epidemic modeling group at Imperial College London and written by 30 scientists on its coronavirus response team, predicted that if the United States had done nothing to prevent the spread of the virus, 2.2 million people could have died. If, however, the government tried to isolate people suspected of having the virus and people they were in contact with, the number of deaths could be cut in half, the researchers said.
They concluded that only a suppression effort across the entire country — an expanded version of efforts now underway across wide swaths of the country — might significantly further reduce the death toll. But they warned that such efforts might have to be maintained for long periods of time in order to ensure that the threat is over.
“The major challenge of suppression,” the British scientists concluded, is the length of time that intensive interventions would be needed, given that “we predict that transmission will quickly rebound if interventions are relaxed.”
Mr. Trump, who spent weeks playing down the threat of the virus — and who has retreated from saying that social distancing could be scaled back in mid-April — congratulated himself at the briefing for projections showing that public health measures may significantly limit the national death toll.
“What would have happened if we did nothing? Because there was a group that said, ‘Let’s just ride it out,’” Mr. Trump said, without saying what “group” he was referring to. The president noted the estimate that as many as 2.2 million people “would have died if we did nothing, if we just carried on with our life.”
“You would have seen people dying on airplanes; you would have seen people dying in hotel lobbies. You would have seen death all over,” Mr. Trump said. By comparison, he said, a potential death toll of 100,000 “is a very low number.”
Models of the spread of any infectious disease often give widely varying estimates of the ultimate death toll. Modelers use different assumptions on how the disease will spread and how much people change their behavior to stop new infections.
The Imperial College model based its estimates on less severe control measures. It estimated as many as 2.2 million deaths if people did not change their behavior at all, and 1.1 million if the county undertook moderate mitigation efforts.
The University of Washington model is considered simple by the standards of the field because it does not take into account the full geographic complexity of the outbreak, nor does it rely on detailed understanding of the basic biology of the disease, said Aaron A. King, a professor in the ecology of infectious disease at the University of Michigan. In the later stages of an outbreak, as some people recover or die from the disease and others change their behavior, more complex models can be more accurate, he said.
Michael D. Shear reported from Washington, and James Glanz from New York. Michael Crowley contributed reporting from Washington.
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