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. “So-called low-risk areas are not to be believed. Bureaucrats everywhere have already begun covering up,” another said.

Such patients, usually found by tracing the contacts of confirmed cases, are quarantined for 14 days and released if they do not show any symptoms. But the number of reports of new cases has started to worry the public.

Documents seen by the South China Morning Post reportedly showed more than 40,000 asymptomatic patients that would not have been included in China’s total number of infections of more than 80,000.

the financial news magazine Caixin called on the government to publish data on asymptomatic carriers. “Within China, transmission caused by asymptomatic infections has occurred many times. The number needs to be made public as soon as possible. Investigation and and research is needed to raise the public’s alertness,” it said.

Last week, authorities formally arrested a man in Beijing who was diagnosed as an asymptomatic carrier in mid-February. He repeatedly visited grocery stores, pharmacies and other public places against regulations. His mother has been infected and 20 other close contacts have now been quarantined.

China’s top respiratory disease expert Zhong Nanshan told the state broadcaster CGTN that while asymptomatic patients who have been in close contact with confirmed patients can be “very infective”, he did not believe they posed a “big problem” in China.

Last week, the premier, Li Keqiang, called on health officials to investigate whether asymptomatic people were contagious, in order to help the country’s ongoing prevention plans, and ordered officials “not to cover up” cases.

But the infectious disease expert Zhang Wenhong, said at a symposium on Friday that asymptomatic carriers would continue to pose a major risk, even as China took measures, such as temporarily banning foreigners from entering the country.

“Now, we only allow Chinese people to come back. But when our country’s doors open again, there will be large numbers coming in. When they are asymptomatic, the risk is great.”

“They got cases,” she noted, “but fewer deaths.”

work on other nonlethal viruses showed that people tend to get less sick with lower doses and more sick with higher doses. A study published in late May involving hamsters, masks and SARS-CoV-2 found those given coverings had milder cases than those who did not get them.

In an article published this month in the Journal of General Internal Medicine, Gandhi noted that in some outbreaks early in the pandemic in which most people did not wear masks, 15 percent of the infected were asymptomatic. But later on, when people began wearing masks, the rate of asymptomatic people was 40 to 45 percent.

She said the evidence points to masks not just protecting others — as U.S. health officials emphasize — but protecting the wearer as well.

The shortfall in testing isn’t just a problem for individual patients and their doctors. It is also holding back large-scale surveys of seemingly healthy populations, in workplaces and elsewhere, and scientific research into fundamental properties of the virus and the disease it causes.

there is an escalating need to test much larger groups repeatedly—to track the spread of the virus as restrictions ease—and to carry out population-based studies that will reveal more about how this virus behaves.

in determining whether an individual is safe to enter a workplace or school on a given morning. Ideally, for the later purposes, tests would be conducted swiftly and at high volume at the places where samples are taken

One such approach, still in development, would exploit the ability of the well-known bacterial gene-editing system known as CRISPR to recognize coronavirus RNA.

While the need for greatly expanded testing in the next phase of this pandemic is widely acknowledged, the United States has no coordinated plan for how to achieve it. The technical building blocks are in hand, but how to put them together is not yet clear. Moreover, major regulatory hurdles limit the use of the results from novel tests in patient care, especially in certain states such as New York. And the logistics of deploying enough personnel to track samples and deliver results are daunting. Because of the complexity and importance of such testing, a centralized program, run by a strong scientific leader and paid for with federal dollars, may be the only solution.

rmed with efficient and accurate tests to detect the virus (indicating active infection) and reliable tests to measure antibodies against it (implying prior exposure and possible immunity), public-health programs could paint an accurate picture of the current pandemic. Small and large businesses, schools, health-care facilities, and other organizations could track the outcomes of their attempts to restore normal activities, and scientists could answer key questions about viral transmission and host immunity.

decisive answers will come only from studying human beings who are exposed to the virus under real-life conditions. Such studies may be feasible only under circumstances in which natural transmission is occurring at significant rates, as it currently is. Therefore, if we are to get answers to the following questions, we must act now.

tudies to answer these questions require identifying enough people who have recovered, then testing them repeatedly for the appearance of a new infection. Such people are relatively easy to find. They include doctors and nurses in hospitals in hard-hit metropolitan areas such as New York City; staff and residents at nursing homes with high rates of infection; and crews of U.S. Navy ships that have experienced outbreaks of COVID-19.

identify asymptomatic infections. Following up on those cases will shed light on how many asymptomatic people ultimately develop symptoms; how long it takes for them to do so; whether asymptomatic people who ultimately develop symptoms have higher viral loads than those who don’t get sick; whether symptomatic and asymptomatic people have different immune responses; whether other, simpler procedures (such as tests for some chemical abnormality in the blood) might be used to screen for infection; and how large a contribution asymptomatic people make to the ongoing transmission of the virus.

Despite repeated warnings after prior epidemics about the likelihood of new ones caused by novel microbes, the United States and many other countries failed to respond efficiently to this one. Scientists might have detected the new coronavirus much earlier with the better tools for microbial surveillance that already exist; prevented the pathogen’s worldwide spread by more aggressive testing and contact tracing; and supported better and safer health care with larger stockpiles and pipelines for procurement of medical equipment. Humanity should never be this unprepared again.

They worried that a vaccine would initially elude scientists, that weary citizens would abandon restrictions despite the risks, that the virus would be with us from now on.

Most experts believed that once the crisis was over, the nation and its economy would revive quickly. But there would be no escaping a period of intense pain.

Exactly how the pandemic will end depends in part on medical advances still to come. It will also depend on how individual Americans behave in the interim. If we scrupulously protect ourselves and our loved ones, more of us will live. If we underestimate the virus, it will find us.

More Americans may die than the White House admits.

The epidemiological model often cited by the White House, which was produced by the University of Washington’s Institute for Health Metrics and Evaluation, originally predicted 100,000 to 240,000 deaths by midsummer. Now that figure is 60,000.

The institute’s projection runs through Aug. 4, describing only the first wave of this epidemic. Without a vaccine, the virus is expected to circulate for years, and the death tally will rise over time.

Fatality rates depend heavily on how overwhelmed hospitals get and what percentage of cases are tested. China’s estimated death rate was 17 percent in the first week of January, when Wuhan was in chaos, according to a Center for Evidence-Based Medicine report, but only 0.7 percent by late February.

Various experts consulted by the Centers for Disease Control and Prevention in March predicted that the virus eventually could reach 48 percent to 65 percent of all Americans, with a fatality rate just under 1 percent, and would kill up to 1.7 million of them if nothing were done to stop the spread.

A model by researchers at Imperial College London cited by the president on March 30 predicted 2.2 million deaths in the United States by September under the same circumstances.

China has officially reported about 83,000 cases and 4,632 deaths, which is a fatality rate of over 5 percent. The Trump administration has questioned the figures but has not produced more accurate ones.

The tighter the restrictions, experts say, the fewer the deaths and the longer the periods between lockdowns. Most models assume states will eventually do widespread temperature checks, rapid testing and contact tracing, as is routine in Asia.

In this country, hospitals in several cities, including New York, came to the brink of chaos.

Only when tens of thousands of antibody tests are done will we know how many silent carriers there may be in the United States. The C.D.C. has suggested it might be 25 percent of those who test positive. Researchers in Iceland said it might be double that.

China is also revising its own estimates. In February, a major study concluded that only 1 percent of cases in Wuhan were asymptomatic. New research says perhaps 60 percent were.

The virus may also be mutating to cause fewer symptoms. In the movies, viruses become more deadly. In reality, they usually become less so, because asymptomatic strains reach more hosts. Even the 1918 Spanish flu virus eventually faded into the seasonal H1N1 flu.

The lockdowns will end, but haltingly.

it is likely a safe bet that at least 300 million of us are still vulnerable.

Until a vaccine or another protective measure emerges, there is no scenario, epidemiologists agreed, in which it is safe for that many people to suddenly come out of hiding. If Americans pour back out in force, all will appear quiet for perhaps three weeks.

The gains to date were achieved only by shutting down the country, a situation that cannot continue indefinitely. The White House’s “phased” plan for reopening will surely raise the death toll no matter how carefully it is executed.

Every epidemiological model envisions something like the dance

On the models, the curves of rising and falling deaths resemble a row of shark teeth.

Surges are inevitable, the models predict, even when stadiums, churches, theaters, bars and restaurants remain closed, all travelers from abroad are quarantined for 14 days, and domestic travel is tightly restricted to prevent high-intensity areas from reinfecting low-intensity ones.

In his wildly popular March 19 article in Medium, “Coronavirus: The Hammer and the Dance,” Tomas Pueyo correctly predicted the national lockdown, which he called the hammer, and said it would lead to a new phase, which he called the dance, in which essential parts of the economy could reopen, including some schools and some factories with skeleton crews.

Even the “Opening Up America Again” guidelines Mr. Trump issued on Thursday have three levels of social distancing, and recommend that vulnerable Americans stay hidden. The plan endorses testing, isolation and contact tracing — but does not specify how these measures will be paid for, or how long it will take to put them in place.

On Friday, none of that stopped the president from contradicting his own message by sending out tweets encouraging protesters in Michigan, Minnesota and Virginia to fight their states’ shutdowns.

China did not allow Wuhan, Nanjing or other cities to reopen until intensive surveillance found zero new cases for 14 straight days, the virus’s incubation period.

Compared with China or Italy, the United States is still a playground.Americans can take domestic flights, drive where they want, and roam streets and parks. Despite restrictions, everyone seems to know someone discreetly arranging play dates for children, holding backyard barbecues or meeting people on dating apps.

Even with rigorous measures, Asian countries have had trouble keeping the virus under control

But if too many people get infected at once, new lockdowns will become inevitable. To avoid that, widespread testing will be imperative.

Reopening requires declining cases for 14 days, the tracing of 90 percent of contacts, an end to health care worker infections, recuperation places for mild cases and many other hard-to-reach goals.

Immunity will become a societal advantage.

Imagine an America divided into two classes: those who have recovered from infection with the coronavirus and presumably have some immunity to it; and those who are still vulnerable.

“It will be a frightening schism,” Dr. David Nabarro, a World Health Organization special envoy on Covid-19, predicted. “Those with antibodies will be able to travel and work, and the rest will be discriminated against.”

Soon the government will have to invent a way to certify who is truly immune. A test for IgG antibodies, which are produced once immunity is established, would make sense

Dr. Fauci has said the White House was discussing certificates like those proposed in Germany. China uses cellphone QR codes linked to the owner’s personal details so others cannot borrow them.

As Americans stuck in lockdown see their immune neighbors resuming their lives and perhaps even taking the jobs they lost, it is not hard to imagine the enormous temptation to join them through self-infection

My daughter, who is a Harvard economist, keeps telling me her age group needs to have Covid-19 parties to develop immunity and keep the economy going,”

It would be a gamble for American youth, too. The obese and immunocompromised are clearly at risk, but even slim, healthy young Americans have died of Covid-19.

The virus can be kept in check, but only with expanded resources.

Resolve to Save Lives, a public health advocacy group run by Dr. Thomas R. Frieden, the former director of the C.D.C., has published detailed and strict criteria for when the economy can reopen and when it must be closed.

once a national baseline of hundreds of thousands of daily tests is established across the nation, any viral spread can be spotted when the percentage of positive results rises.

To keep the virus in check, several experts insisted, the country also must start isolating all the ill — including mild cases.

“If I was forced to select only one intervention, it would be the rapid isolation of all cases,”

In China, anyone testing positive, no matter how mild their symptoms, was required to immediately enter an infirmary-style hospital — often set up in a gymnasium or community center outfitted with oxygen tanks and CT scanners.

There, they recuperated under the eyes of nurses. That reduced the risk to families, and being with other victims relieved some patients’ fears.

Still, experts were divided on the idea of such wards

Ultimately, suppressing a virus requires testing all the contacts of every known case. But the United States is far short of that goal.

In China’s Sichuan Province, for example, each known case had an average of 45 contacts.

The C.D.C. has about 600 contact tracers and, until recently, state and local health departments employed about 1,600, mostly for tracing syphilis and tuberculosis cases.

China hired and trained 9,000 in Wuhan alone. Dr. Frieden recently estimated that the United States will need at least 300,000.

There will not be a vaccine soon.

any effort to make a vaccine will take at least a year to 18 months.

the record is four years, for the mumps vaccine.

for unclear reasons, some previous vaccine candidates against coronaviruses like SARS have triggered “antibody-dependent enhancement,” which makes recipients more susceptible to infection, rather than less. In the past, vaccines against H.I.V. and dengue have unexpectedly done the same.

A new vaccine is usually first tested in fewer than 100 young, healthy volunteers. If it appears safe and produces antibodies, thousands more volunteers — in this case, probably front-line workers at the highest risk — will get either it or a placebo in what is called a Phase 3 trial.

It is possible to speed up that process with “challenge trials.” Scientists vaccinate small numbers of volunteers, wait until they develop antibodies, and then “challenge” them with a deliberate infection to see if the vaccine protects them.

Normally, it is ethically unthinkable to challenge subjects with a disease with no cure, such as Covid-19.

“Fewer get harmed if you do a challenge trial in a few people than if you do a Phase 3 trial in thousands,” said Dr. Lipsitch, who recently published a paper advocating challenge trials in the Journal of Infectious Diseases. Almost immediately, he said, he heard from volunteers.

The hidden danger of challenge trials, vaccinologists explained, is that they recruit too few volunteers to show whether a vaccine creates enhancement, since it may be a rare but dangerous problem.

if a vaccine is invented, the United States could need 300 million doses — or 600 million if two shots are required. And just as many syringes.

“People have to start thinking big,” Dr. Douglas said. “With that volume, you’ve got to start cranking it out pretty soon.”

Treatments are likely to arrive first.

The modern alternative is monoclonal antibodies. These treatment regimens, which recently came very close to conquering the Ebola epidemic in eastern Congo, are the most likely short-term game changer, experts said.

as with vaccines, growing and purifying monoclonal antibodies takes time. In theory, with enough production, they could be used not just to save lives but to protect front-line workers.

Having a daily preventive pill would be an even better solution, because pills can be synthesized in factories far faster than vaccines or antibodies can be grown and purified.

Goodbye, ‘America First.’

A public health crisis of this magnitude requires international cooperation on a scale not seen in decades. Yet Mr. Trump is moving to defund the W.H.O., the only organization capable of coordinating such a response.

And he spent most of this year antagonizing China, which now has the world’s most powerful functioning economy and may become the dominant supplier of drugs and vaccines. China has used the pandemic to extend its global influence, and says it has sent medical gear and equipment to nearly 120 countries.

This is not a world in which “America First” is a viable strategy, several experts noted.

“If President Trump cares about stepping up the public health efforts here, he should look for avenues to collaborate with China and stop the insults,”

If we alienate the Chinese with our rhetoric, I think it will come back to bite us,” he said.“What if they come up with the first vaccine? They have a choice about who they sell it to. Are we top of the list? Why would we be?”

Once the pandemic has passed, the national recovery may be swift. The economy rebounded after both world wars, Dr. Mulder noted.

In one of the most provocative analyses in his follow-up article, “Coronavirus: Out of Many, One,” Mr. Pueyo analyzed Medicare and census data on age and obesity in states that recently resisted shutdowns and counties that voted Republican in 2016.

He calculated that those voters could be 30 percent more likely to die of the virus.

In the periods after both wars, Dr. Mulder noted, society and incomes became more equal. Funds created for veterans’ and widows’ pensions led to social safety nets, measures like the G.I. Bill and V.A. home loans were adopted, unions grew stronger, and tax benefits for the wealthy withered.

If a vaccine saves lives, many Americans may become less suspicious of conventional medicine and more accepting of science in general — including climate change

COVID-19 testing has been an unmitigated failure in this country.

Rather than growing rapidly—as all experts think is absolutely necessary—the daily number of tests administered in some jurisdictions has even decreased. In New York, for instance, 10,241 tests were performed on April 6, but supply limits forced a huge drop a few days later to 25 total tests.

Quest Diagnostics, one of the two biggest firms that run tests, just furloughed 9 percent of its workforce. In addition, news reports suggest that, as of last week, 90 percent of the 15-minute tests developed by Abbott Laboratories are idle due to a lack of necessary reagents and qualified personnel

How many tests do we need in order to safely relax social-distancing measures, reopen nonessential businesses and schools, and allow large gatherings

we should be conducting a minimum of 500,000 tests a day.

Paul Romer, has called for the capacity to run 20 million to 30 million tests a day

Even this has been criticized as insufficient for the task of identifying enough of the asymptomatic spreaders to keep the pandemic in check.

Current guidelines from the Centers for Disease Control and Prevention give priority first to hospitalized patients and symptomatic health-care workers, then to high-risk patients

ptomatic individuals are not tested, even if they had contact with people who tested positive.

This is an enormous mistake. If we want to control the spread of COVID-19, the United States must adopt a new testing policy that prioritizes people who, although asymptomatic, may have the virus and infect many others.

We should target four groups. First, all health-care workers and other first responders who directly interact with many people

The fourth group would include all those who are planning to return to the workplace. These are precisely the individuals without symptoms whom the CDC recommends against testing.

The next group would be potential “super-spreaders”—asymptomatic individuals who could come into contact with many people. This third group would include people in large families and those who must interact with many vulnerable people, such as employees of long-term-care facilities

Second, workers who maintain our supply chains and crucial infrastructure, including grocery-store workers, police officers, public-transit workers, and sanitation personnel.

Not testing suspected COVID-19 patients will not harm those patients

Symptomatic patients should be tested only in the rare case where a positive test would meaningfully change what type of care is delivered.

To shift the focus of testing away from the sickest patients and toward the people most likely to spread the coronavirus, we will have to conduct millions of tests a day.

How can we close this gap between our needs and current capacity? We need a national strategy over the next 10 weeks, one that draws on the many strengths of our research system

We also need to encourage rapid adoption of the saliva test that now has an emergency approval from the FDA and expedite the approval of tests that require fewer reagents and staff.

Another promising pathway is to pool many tests and run them together. If a pooled sample tests negative, everyone in the pool is negative. If it is positive, the members of the pool can be tested individually

A more sophisticated version of this approach uses genetic “bar codes” that make it possible to trace back which of the many samples in a pool was the one that had RNA from the virus, without any retesting.

How can we get this testing capacity up and running? One idea is for Congress to award in the next stimulus bill, say, $150 million in unrestricted research funds to the first five universities that can process 10 million tests in a week or less

Another catalyst could be to subsidize businesses that agree to test all their employees as they return to work

When someone tests positive, officials should identify close contacts, find them, and test them. To do the tracing, we may need to hire 100,000 to 200,000 additional public-health workers.

This type of voluntary contact tracing is labor-intensive and requires some training, but it does not require highly specialized skills

If we adopt and follow a coherent plan, we can have a testing regime that keeps us safe without compromising our freedoms

Ventilation systems in schools, nursing homes, residences and businesses may need to minimize recirculating air and add powerful new filters.

in an open letter to the W.H.O., 239 scientists in 32 countries have outlined the evidence showing that smaller particles can infect people, and are calling for the agency to revise its recommendations

Whether carried aloft by large droplets that zoom through the air after a sneeze, or by much smaller exhaled droplets that may glide the length of a room, these experts said, the coronavirus is borne through air and can infect people when inhaled

But the infection prevention and control committee in particular, experts said, is bound by a rigid and overly medicalized view of scientific evidence, is slow and risk-averse in updating its guidance and allows a few conservative voices to shout down dissent.

“If we started revisiting airflow, we would have to be prepared to change a lot of what we do,” she said. “I think it’s a good idea, a very good idea, but it will cause an enormous shudder through the infection control society.”

In early April, a group of 36 experts on air quality and aerosols urged the W.H.O. to consider the growing evidence on airborne transmission of the coronavirus. The agency responded promptly, calling Lidia Morawska, the group’s leader and a longtime W.H.O. consultant, to arrange a meeting.

But the discussion was dominated by a few experts who are staunch supporters of handwashing and felt it must be emphasized over aerosols, according to some participants, and the committee’s advice remained unchanged.

Dr. Morawska and others pointed to several incidents that indicate airborne transmission of the virus, particularly in poorly ventilated and crowded indoor spaces. They said the W.H.O. was making an artificial distinction between tiny aerosols and larger droplets, even though infected people produce both.

We’ve known since 1946 that coughing and talking generate aerosols,

Scientists have not been able to grow the coronavirus from aerosols in the lab.

Most of the samples in those experiments have come from hospital rooms with good air flow that would dilute viral levels.

In most buildings, she said, “the air-exchange rate is usually much lower, allowing virus to accumulate in the air and pose a greater risk.”

The W.H.O. also is relying on a dated definition of airborne transmission, Dr. Marr said. The agency believes an airborne pathogen, like the measles virus, has to be highly infectious and to travel long distances.

Dr. Marr and others said the coronavirus seemed to be most infectious when people were in prolonged contact at close range, especially indoors, and even more so in superspreader events — exactly what scientists would expect from aerosol transmission.

Experts all agree that the coronavirus does not behave that way.

“We have this notion that airborne transmission means droplets hanging in the air capable of infecting you many hours later, drifting down streets, through letter boxes and finding their way into homes everywhere,”

The agency lagged behind most of its member nations in endorsing face coverings for the public. While other organizations, including the C.D.C., have long since acknowledged the importance of transmission by people without symptoms, the W.H.O. still maintains that asymptomatic transmission is rare.

Many experts said the W.H.O. should embrace what some called a “precautionary principle” and others called “needs and values” — the idea that even without definitive evidence, the agency should assume the worst of the virus, apply common sense and recommend the best protection possible.

“There is no incontrovertible proof that SARS-CoV-2 travels or is transmitted significantly by aerosols, but there is absolutely no evidence that it’s not,

So at the moment we have to make a decision in the face of uncertainty, and my goodness, it’s going to be a disastrous decision if we get it wrong,” she said. “So why not just mask up for a few weeks, just in case?”

he agency also must consider the needs of all its member nations, including those with limited resources, and make sure its recommendations are tempered by “availability, feasibility, compliance, resource implications,” she said.

if the W.H.O. were to push for rigorous control measures in the absence of proof, hospitals in low- and middle-income countries may be forced to divert scarce resources from other crucial programs.

That’s the balance that an organization like the W.H.O. has to achieve,” he said. “It’s the easiest thing in the world to say, ‘We’ve got to follow the precautionary principle,’ and ignore the opportunity costs of that.”

In interviews, other scientists criticized this view as paternalistic. “‘We’re not going to say what we really think, because we think you can’t deal with it?’ I don’t think that’s right,”

Even cloth masks, if worn by everyone, can significantly reduce transmission, and the W.H.O. should say so clearly, he added.

The W.H.O. tends to describe “an absence of evidence as evidence of absence,” Dr. Aldis added. In April, for example, the W.H.O. said, “There is currently no evidence that people who have recovered from Covid-19 and have antibodies are protected from a second infection.”

The statement was intended to indicate uncertainty, but the phrasing stoked unease among the public and earned rebukes from several experts and journalists. The W.H.O. later walked back its comments.

In a less public instance, the W.H.O. said there was “no evidence to suggest” that people with H.I.V. were at increased risk from the coronavirus. After Joseph Amon, the director of global health at Drexel University in Philadelphia who has sat on many agency committees, pointed out that the phrasing was misleading, the W.H.O. changed it to say the level of risk was “unknown.”

But W.H.O. staff and some members said the critics did not give its committees enough credit.“Those that may have been frustrated may not be cognizant of how W.H.O. expert committees work, and they work slowly and deliberately,”

The World Health Organization and the Centers for Disease Control and Prevention continue to state that masks don’t necessarily protect healthy individuals from getting infected as they go about their daily lives.

While wearing a mask may not necessarily prevent healthy people from getting sick, and it certainly doesn’t replace important measures such as hand-washing or social distancing, it may be better than nothing, Dr. Atmar said.

the recent surge in infections in the United States, which has put the country at the center of the epidemic, with more confirmed cases than China,

“The swift increase in cases to these levels in the U.S. highlights to an even greater degree the importance of implementing and adhering to public health measures,”

The official guidance continues to recommend that masks should be reserved for people who are already sick,

But studies of influenza pandemics have shown that when high-grade N95 masks are not available, surgical masks do protect people a bit more than not wearing masks at all.

With the current coronavirus, researchers are also finding that there are more asymptomatic cases than were known early on in the pandemic.

“It’s still hard to tell what percentage of people are truly asymptomatic because many go on to develop symptoms a few days later,” said Dr. Neil Fishman, the chief medical officer of the Hospital of the University of Pennsylvania.

The first warning sign came when case numbers, after weeks of steep declines, appeared to level off -- with the country still averaging tens of thousands of new cases daily.

But governors cited fewer Covid-19 cases and more vaccinations while lifting measures aimed at curbing the spread of the virus.

Chicago officials earlier this month raised indoor capacity for bars, restaurants and other businesses and Baltimore leaders announced Wednesday they were easing restrictions on places including religious facilities, retail stores and malls, fitness centers and food service establishments -- changes that will go into effect next week.

Delaware, Montana, Alabama and West Virginia have also seen big increases.

The B.1.1.7 variant, she said this week, is projected to become the dominant variant in the US by the end of this month or early April.Despite the warnings, spring break crowds are gathering -- with Florida officials reporting too many people and not enough masks -- and nationwide, air travel numbers are hitting pandemic-era records.

Now, as the country inches closer to 30 million reported infections, cases are rising by more than 10% in 14 states this week compared to last week,

We're in a race to get the population vaccinated. At the same time, we're fighting people's exhaustion with the restrictions that public health has put in place and we're fighting the move by so many governors to remove the restrictions that are keeping us all safe."

Michigan cases are increasing the fastest, with more than a 50% jump this week compared to last,

All that while cases of the worrying variants -- notably the highly contagious B.1.1.7 variant -- climbed. The variants have the potential to wipe out all the progress the US made if Americans get lax with safety measures,

There's a long list of factors contributing to the spike in cases in Michigan,

Those include the rolling back of restrictions, a prison outbreak, Covid-19 fatigue, a failure to wear masks, and the B.1.1.7 variant fueling the surge, Morse told CNN. Michigan Gov. Gretchen Whitmer eased restrictions earlier this month, upping capacity limits at restaurants as well as in retail stores, gyms and other facilities.

In West Virginia, Gov. Jim Justice said Wednesday that Covid-19 hospitalizations have "jumped up" slightly

Justice had eased restrictions earlier this month, increasing capacity at bars, restaurants and other businesses to 100% and upping the social-gathering limit.

During Wednesday's news briefing, he added that the state has had "seven outbreaks in our church community" across five counties.

what could play a key role in helping control the pandemic will be more accessible, inexpensive coronavirus tests, top health officials

"I do believe that once we have teachers vaccinated that we can use testing in the schools -- serial testing, cadence testing -- to identify potential infections, asymptomatic infections, shut down clusters and keep our schools open."

Her remarks came the same day the CDC released updated guidance about testing, saying more and better testing should help catch asymptomatic cases and control the spread.

More than 73.6 million Americans have received at least one dose of a Covid-19 vaccine, according to CDC data. And more than 39.9 million people are fully vaccinated -- roughly 12% of the US population. But challenges -- including vaccine hesitancy, disinformation and inequities -- remain, and it's not entirely clear when the US will hit herd immunity -

On Wednesday, both Fauci and Walensky pushed back against questions about herd immunity, saying a lot depended on how quickly Americans take vaccines.

For now, the US still has a long way to go to overcome vaccine hesitancy,

Vaccination is the country's best hope to get beyond the pandemic, he said, "and yet there's all this overlay, and some of it is politics and some of it's social media conspiracy theories and some of it is just distrust of anything that the government had anything to do with."

Additionally, in the first two and half months of vaccine distribution, counties considered to have high social vulnerability had lower vaccine coverage than counties considered to have low social vulnerability,

The agency's social vulnerability index identifies communities that may need additional support during emergencies based on more than a dozen indicators across four categories: socioeconomic status, household composition, racial/ethnic minority status and housing type.

By March 1, vaccination coverage was about 2 percentage points higher in counties with low social vulnerability than in counties with high social vulnerability -- and the differences were largely driven by socioeconomic disparities, particularly differences in the share of the population with a high school diploma and per capita income.

Only five states -- Arizona, Montana, Alaska, Minnesota and West Virginia -- had higher coverage in counties with high social vulnerability.

Achieving vaccine equity, the CDC said, is an important goal requiring "preferential access and administration to those who have been most affected"

Dr. Nettles said on Tuesday that a total of 20 million doses would be ready by the end of March. The company has a contract to deliver 100 million doses by the end of June.

Johnson & Johnson looked for asymptomatic infections by checking for coronavirus antibodies 71 days after volunteers got a vaccine or a placebo. The new analyses estimate that the vaccine has an efficacy rate of 74 percent against asymptomatic infections. But that calculation was based on a relatively small number of volunteers, and the F.D.A. noted that “There is uncertainty about the interpretation of these data and definitive conclusions cannot be drawn at this time.”“I think it’s going to add to the growing evidence that the vaccines really do prevent infection as well as prevent disease,” Dr. Barouch said.

0.6 percent of the world’s population is 47 million people, and 0.6 percent of the American population is 2 million people. The virus remains a major threat.

China had reported 90,294 cases as of Friday and 4,634 deaths, which is a C.F.R. of 5 percent. The United States was very close to that mark. It has had 2,811,447 cases and 129,403 deaths, about 4.6 percent

But their case fatality rates vary wildly: Iceland’s is less than 1 percent, New Zealand’s and Israel’s are below 2 percent. Belgium, by comparison, is at 16 percent, and Italy and Britain at 14 percent

it is difficult to measure fatality rates during pandemics, especially at the beginning.

In the chaos that ensues when a new virus hits a city hard, thousands of people may die and be buried without ever being tested, and certainly without them all being autopsied.

Normally, once the chaos has subsided, more testing is done and more mild cases are found — and because the denominator of the fraction rises, fatality rates fall. But the results are not always consistent or predictable.

Ten sizable countries, most of them in Western Europe, have tested bigger percentages of their populations than has the United States, according to Worldometer, which gathers statistics. They are Iceland, Denmark, Spain, Portugal, Belgium, Ireland, Italy, Britain, Israel and New Zealand.

So far, in most countries, about 20 percent of all confirmed Covid-19 patients become ill enough to need supplemental oxygen or even more advanced hospital care

In each of the eight influenza pandemics to hit the United States since 1763, a relatively mild first wave — no matter what time of year it arrived — was followed by a larger, much more lethal wave a few months later

Whether those patients survive depends on a host of factors, including age, underlying illnesses and the level of medical care available.

Death rates are expected to be lower in countries with younger populations and less obesity, which are often the poorest countries. Conversely, the figures should be higher in countries that lack oxygen tanks, ventilators and dialysis machines, and where many people live far from hospitals. Those are also often the poorest countries.

new evidence that people with Type A blood are more likely to fall deathly ill could change risk calculations. Type A blood is relatively rare in West Africa and South Asia, and very rare among the Indigenous peoples of South America.

it had relied on a mix of data sent in by member countries and by academic groups, and on a meta-analysis done in May by scientists at the University of Wollongong and James Cook University in Australia.

Those researchers looked at 267 studies in more than a dozen countries, and then chose the 25 they considered the most accurate, weighting them for accuracy and averaged the data. They concluded that the global I.F.R. was 0.64 percent.

The 25 studies that the Australian researchers considered the most accurate relied on very different methodologies. One report, for example, was based on diagnostic PCR tests of all passengers and crew aboard the Diamond Princess, the cruise ship that docked in Japan after it was overcome by the coronavirus. Another study drew data from an antibody survey of 38,000 Spaniards, while another included only 1,104 Swedes.

To arrive at the C.D.C.’s new estimate, researchers tested samples from 11,933 people for antibodies to the coronavirus in six regions in the United States. New York City reported 53,803 cases by April 1, but the actual number of infections was 12 times higher — nearly 642,000, the agency estimated.

The global fatality rates could still change. With one or two exceptions, like Iran and Ecuador, the pandemic first struck wealthier countries in Asia, Western Europe and North America where advanced medical care was available.

Many experts fear that infections and deaths will shoot up in the fall as colder weather forces people indoors, where they are more likely to infect one another. Discipline about wearing masks and avoiding breathing on one another will be even more important then.

Those percentages are far higher rates than the 2.5 percent death rate often ascribed to the 1918 flu pandemic.

More than a third of all the people killed by the Spanish flu, which lasted from March 1918 to late 1920, died in the short stretch between September and December 1918 — about six months after a first, relatively mild version of what may have been the same virus broke out in western Kansas.

if healthy individuals start stockpiling surgical masks and high-grade N95 masks, they can also make it harder for health workers to get the resources they need to help on the front lines.

But studies of influenza pandemics have shown that when high-grade N95 masks are not available, surgical masks do protect people a bit more than not wearing masks at all. And when masks are combined with hand hygiene, they help reduce the transmission of infections.

When researchers conducted systematic review of a variety of interventions used during the SARS outbreak in 2003, they found that washing hands more than 10 times daily was 55 percent effective in stopping virus transmission, while wearing a mask was actually more effective — at about 68 percent

Wearing gloves offered about the same amount of protection as frequent hand-washing, and combining all measures — hand-washing, masks, gloves and a protective gown — increased the intervention effectiveness to 91 percent.

Classified data from the Chinese government that was reported in the South China Morning Post indicated that up to a third of all people who tested positive for the coronavirus could have been silent carriers.

Widespread testing on the Diamond Princess showed that half of the positive cases on board the cruise ship had no symptoms.

A new report from the C.D.C., published Friday, also suggests that several residents of a nursing facility in King County, Washington, either did not have any symptoms or developed very mild symptoms only after they had been confirmed to have a coronavirus infection.

“It’s still hard to tell what percentage of people are truly asymptomatic because many go on to develop symptoms a few days later,

“What we do know is that individuals can shed virus about 48 hours before they develop symptoms and masking can prevent transmission from those individuals.”

Wearing a mask can also reduce the likelihood that people will touch their face

In many Asian countries, everyone is encouraged to wear masks, and the approach is about crowd psychology and protection. If everyone wears a mask, individuals protect each other, reducing overall community transmission

The sick automatically have one on and are also more likely to adhere to keeping their mask on because the stigma of wearing one is removed.

Masks are also an important signal that it’s not business as usual during a pandemic

They may also serve as an act of solidarity, showing that all citizens are on board with the precautionary measures needed to bring infections under control.

“If everyone in the community wears a mask, it could decrease transmission,” Dr. Fishman said. “But unfortunately I think that we don’t have enough masks to make that effective policy in the U.S.”

Lena Einhorn, a virologist who has been one of the leading domestic critics of Sweden’s coronavirus policy, told the Observer that the government and the health agency were still resisting the most obvious explanations.

The agency’s advice to those managing and working at nursing homes, like its policy towards coronavirus in general, has been based on its judgment that the “spread from those without symptoms is responsible for a very limited share” of those who get infected.

Its advice to the care workers and nurses looking after older people such as Bondesson’s 69-year-old mother is that they should not wear protective masks or use other protective equipment unless they are dealing with a resident in the home they have reason to suspect is infected.

the central protective measure in place is that staff should stay home if they detect any symptoms in themselves.

Based on this seroprevalence data, the authors estimate that in Santa Clara County the true infection fatality rate is somewhere in the range of 0.12% to 0.2%—far closer to seasonal influenza than to the original, case-based estimates.

In New York City, a study published in the New England Journal of Medicine examined 215 women entering two hospitals to give birth between March 22 and April 4. These patients had a Covid-19 infection rate over 15%. Of expectant mothers who tested positive for active infections, 88% were asymptomatic at the time of admission. That infection rate is about 10 times the rate of known cases in the city

Similar proportions of infections to cases are now being discovered around the world: 30 times in Robbio, Italy; 10 times in Iceland; 14 times in Gangelt, Germany; 27 times in Denmark. Germany and Denmark are now leading Europe in reopening their economies in the coming week

a path forward demands continued monitoring of seroprevalence as well as new case testing, identifying and protecting those most vulnerable to more serious or even fatal infections, and supporting hospital capacity to handle surges of respiratory intensive-care patients.

The science to support better modeling and decision making is rapidly becoming available. One hopes that it will inform better policy decisions.

There might be other explanations. With any infection, there are four basic questions to ask when looking at broad differences in death rates. Is the virus different here versus there? NO. Right now, there is no evidence that the virus is mutating toward a more potent strain in the US.Is one country diagnosing the virus sooner than another? YES. As above, this may be skewing German and South Korean results by identifying asymptomatic and mildly symptomatic persons unlikely to require medical care. Hospitalization rates by country, currently not tracked, would help sort out the contribution of aggressive testing to survival rates. Is the infected patient different here versus there? YES. South Korea (young patients) and Italy (old patients) are unique in the outbreak, and the characteristics in Iran are not well known. All other countries with specific information, from China to even the US epicenter of New York City, have shown the same basic distribution with respect to age, sex (more men than women) and smoking. Is the health care system different here versus there? OH YES. Health care system differences at the country level are hard to examine: information is sparse and, given the 50,000-foot view, possibly misleading. However, health care experts typically can rely on "structural measures" to determine the quality of a hospital or a state or a country.

The World Bank tracks health care information by country on three relevant structural measures (though recentness of information varies country to country), each measured per 1,000 general population: doctors, nurses and hospital beds. They and other sources also track two other relevant variables: lifespan per country and health care spending per individual. Neither of these demonstrate differences in affected Western European countries that might explain a difference in Covid-19 survival.

Among the nine countries with the highest number of Covid-19 cases, the country that has the highest nurse rate also has the lowest death rate from the disease. Germany has 13.2 nurses per 1,000 (echoing a trend for high nurse numbers throughout Northern Europe) far above the other heavily Covid-19 affected countries. This may be just another armchair epidemiologist observation of course. But higher numbers of nurses may reflect one of two beneficial factors (or both): first, that nurses, the backbone of hospital (and especially ICU) care, are essential to patient management and, ultimately, survival.

Either way, it is a reminder that Covid-19 will continue to reveal the strengths and weaknesses of health care systems across the world. The current observed differences also mandate that, when we finally are out from underneath the weight of the current crisis, we must work to determine how we can deliver better health care to large populations across the world.

the coronavirus more often infects clusters of family members, friends and work colleagues,

“You can contain clusters,” Dr. Heymann said. “You need to identify and stop discrete outbreaks, and then do rigorous contact tracing.”

The microphone should not even be at the White House, scientists said, so that briefings of historic importance do not dissolve into angry, politically charged exchanges with the press corps, as happened again on Friday.

Americans must be persuaded to stay home, they said, and a system put in place to isolate the infected and care for them outside the home

Travel restrictions should be extended, they said; productions of masks and ventilators must be accelerated, and testing problems must be resolved.

It was not at all clear that a nation so fundamentally committed to individual liberty and distrustful of government could learn to adapt to many of these measures, especially those that smack of state compulsion.

What follows are the recommendations offered by the experts interviewed by The Times.

they were united in the opinion that politicians must step aside and let scientists both lead the effort to contain the virus and explain to Americans what must be done.

medical experts should be at the microphone now to explain complex ideas like epidemic curves, social distancing and off-label use of drugs.

doing so takes intelligent, rapidly adaptive work by health officials, and near-total cooperation from the populace. Containment becomes realistic only when Americans realize that working together is the only way to protect themselves and their loved ones.

Above all, the experts said, briefings should focus on saving lives and making sure that average wage earners survive the coming hard times — not on the stock market, the tourism industry or the president’s health.

“At this point in the emergency, there’s little merit in spending time on what we should have done or who’s at fault,”

The next priority, experts said, is extreme social distancing.If it were possible to wave a magic wand and make all Americans freeze in place for 14 days while sitting six feet apart, epidemiologists say, the whole epidemic would sputter to a halt.

The virus would die out on every contaminated surface and, because almost everyone shows symptoms within two weeks, it would be evident who was infected. If we had enough tests for every American, even the completely asymptomatic cases could be found and isolated.

The crisis would be over.

Obviously, there is no magic wand, and no 300 million tests. But the goal of lockdowns and social distancing is to approximate such a total freeze.

In contrast to the halting steps taken here, China shut down Wuhan — the epicenter of the nation’s outbreak — and restricted movement in much of the country on Jan. 23, when the country had a mere 500 cases and 17 deaths.Its rapid action had an important effect: With the virus mostly isolated in one province, the rest of China was able to save Wuhan.

Even as many cities fought their own smaller outbreaks, they sent 40,000 medical workers into Wuhan, roughly doubling its medical force.

Stop transmission within cities

the weaker the freeze, the more people die in overburdened hospitals — and the longer it ultimately takes for the economy to restart.

People in lockdown adapt. In Wuhan, apartment complexes submit group orders for food, medicine, diapers and other essentials. Shipments are assembled at grocery warehouses or government pantries and dropped off. In Italy, trapped neighbors serenade one another.

Each day’s delay in stopping human contact, experts said, creates more hot spots, none of which can be identified until about a week later, when the people infected there start falling ill.

South Korea avoided locking down any city, but only by moving early and with extraordinary speed. In January, the country had four companies making tests, and as of March 9 had tested 210,000 citizens — the equivalent of testing 2.3 million Americans.

As of the same date, fewer than 9,000 Americans had been tested.

Fix the testing mess

Testing must be done in a coordinated and safe way, experts said. The seriously ill must go first, and the testers must be protected.In China, those seeking a test must describe their symptoms on a telemedicine website. If a nurse decides a test is warranted, they are directed to one of dozens of “fever clinics” set up far from all other patients.

Isolate the infected

As soon as possible, experts said, the United States must develop an alternative to the practice of isolating infected people at home, as it endangers families. In China, 75 to 80 percent of all transmission occurred in family clusters.

Cellphone videos from China show police officers knocking on doors and taking temperatures. In some, people who resist are dragged away by force. The city of Ningbo offered bounties of $1,400 to anyone who turned in a coronavirus sufferer.

In China, said Dr. Bruce Aylward, leader of the World Health Organization’s observer team there, people originally resisted leaving home or seeing their children go into isolation centers with no visiting rights — just as Americans no doubt would.

In China, they came to accept it.“They realized they were keeping their families safe,” he said. “Also, isolation is really lonely. It’s psychologically difficult. Here, they were all together with other people in the same boat. They supported each other.”

Find the fevers

Make masks ubiquitous

In China, having a fever means a mandatory trip to a fever clinic to check for coronavirus. In the Wuhan area, different cities took different approaches.

In most cities in affected Asian countries, it is commonplace before entering any bus, train or subway station, office building, theater or even a restaurant to get a temperature check. Washing your hands in chlorinated water is often also required.

The city of Qianjiang, by contrast, offered the same amount of money to any resident who came in voluntarily and tested positive

Voluntary approaches, like explaining to patients that they will be keeping family and friends safe, are more likely to work in the West, she added.

Trace the contacts

Finding and testing all the contacts of every positive case is essential, experts said. At the peak of its epidemic, Wuhan had 18,000 people tracking down individuals who had come in contact with the infected.

Dr. Borio suggested that young Americans could use their social networks to “do their own contact tracing.” Social media also is used in Asia, but in different ways

When he lectured at a Singapore university, Dr. Heymann said, dozens of students were in the room. But just before he began class, they were photographed to record where everyone sat.

Instead of a policy that advises the infected to remain at home, as the Centers for Disease and Prevention now does, experts said cities should establish facilities where the mildly and moderately ill can recuperate under the care and observation of nurses.

There is very little data showing that flat surgical masks protect healthy individuals from disease. Nonetheless, Asian countries generally make it mandatory that people wear them.

The Asian approach is less about data than it is about crowd psychology, experts explained.All experts agree that the sick must wear masks to keep in their coughs. But if a mask indicates that the wearer is sick, many people will be reluctant to wear one. If everyone is required to wear masks, the sick automatically have one on and there is no stigma attached.

Also, experts emphasized, Americans should be taught to take seriously admonitions to stop shaking hands and hugging

Preserve vital services

Only the federal government can enforce interstate commerce laws to ensure that food, water, electricity, gas, phone lines and other basic needs keep flowing across state lines to cities and suburbs

“I sense that most people — and certainly those in business — get it. They would prefer to take the bitter medicine at once and contain outbreaks as they start rather than gamble with uncertainty.”

Produce ventilators and oxygen

The manufacturers, including a dozen in the United States, say there is no easy way to ramp up production quickly. But it is possible other manufacturers, including aerospace and automobile companies, could be enlisted to do so.

Canadian nurses are disseminating a 2006 paper describing how one ventilator can be modified to treat four patients simultaneously. Inventors have proposed combining C-PAP machines, which many apnea sufferers own, and oxygen tanks to improvise a ventilator.

One of the lessons of China, he noted, was that many Covid-19 patients who would normally have been intubated and on ventilators managed to survive with oxygen alone.

Retrofit hospitals

In Wuhan, the Chinese government famously built two new hospitals in two weeks. All other hospitals were divided: 48 were designated to handle 10,000 serious or critical coronavirus patients, while others were restricted to handling emergencies like heart attacks and births.

Wherever that was impractical, hospitals were divided into “clean” and “dirty” zones, and the medical teams did not cross over. Walls to isolate whole wards were built

Decide when to close schools

Recruit volunteers

China’s effort succeeded, experts said, in part because of hundreds of thousands of volunteers. The government declared a “people’s war” and rolled out a “Fight On, Wuhan! Fight On, China!” campaign.

Many people idled by the lockdowns stepped up to act as fever checkers, contact tracers, hospital construction workers, food deliverers, even babysitters for the children of first responders, or as crematory workers.

“In my experience, success is dependent on how much the public is informed and participates,” Admiral Ziemer said. “This truly is an ‘all hands on deck’ situation.”

Prioritize the treatments

Clinicians in China, Italy and France have thrown virtually everything they had in hospital pharmacies into the fight, and at least two possibilities have emerged that might save patients: the anti-malaria drugs chloroquine and hydroxychloroquine, and the antiviral remdesivir, which has no licensed use.

An alternative is to harvest protective antibodies from the blood of people who have survived the illness,

The purified blood serum — called immunoglobulin — could possibly be used in small amounts to protect emergency medical workers, too.

“Unfortunately, the first wave won’t benefit from this,” Dr. Hotez said. “We need to wait until we have enough survivors.”Find a vaccine

testing those candidate vaccines for safety and effectiveness takes time.

The roadblock, vaccine experts explained, is not bureaucratic. It is that the human immune system takes weeks to produce antibodies, and some dangerous side effects can take weeks to appear.

After extensive animal testing, vaccines are normally given to about 50 healthy human volunteers to see if they cause any unexpected side effects and to measure what dose produces enough antibodies to be considered protective.

If that goes well, the trial enrolls hundreds or thousands of volunteers in an area where the virus is circulating. Half get the vaccine, the rest do not — and the investigators wait. If the vaccinated half do not get the disease, the green light for production is finally given.

In the past, some experimental vaccines have produced serious side effects, like Guillain-Barre syndrome, which can paralyze and kill. A greater danger, experts said, is that some experimental vaccines, paradoxically, cause “immune enhancement,” meaning they make it more likely, not less, that recipients will get a disease. That would be a disaster.

One candidate coronavirus vaccine Dr. Hotez invented 10 years ago in the wake of SARS, he said, had to be abandoned when it appeared to make mice more likely to die from pneumonia when they were experimentally infected with the virus.

Reach out to other nations

• Testing. The CDC develops tests for its own internal use. The Food and Drug Administration requires that tests offered to the public be proved safe and effective. Government might have said “have at it, boys” and allowed anyone to make and sell anything and call it a Covid-19 test. This wouldn’t have been government.

• Testing, again. A MacGuffin that many countries, including the U.S., are converging on is constant and widespread testing to quarantine new cases. Testing will allow us to “flatten the curve” while lifting the stay-at-home orders and permit commerce to revive.

• The lockdowns. Imagine a problem that can be solved by holding your head underwater but stops being solved when you lift your head out. This is no solution. How can any society lift its stay-at-home order if there’s no vaccine and most people remain uninfected? Not even the Chinese, as we are about to learn, really have an answer

By now even the most tunnel-visioned epidemiologist must admit the lockdown cure will soon be worse than the disease, imposing social destruction beyond imagining.

Though the Trump administration is guilty of testing stumbles, unrealistic is the notion that enough testing could have been made available to contain a novel flu-like virus once it was widely established.

This probably is a polite fiction but it will let us get the economy mostly open. In reality, we will end up throwing a variety of strategies at a persistent epidemic (testing, treatments, voluntary social distancing) and accept what nature gives us.

And government will keep pouring resources into health care so we can at least believe every victim is getting a fair shot at survival.

• The death rate. Given asymptomatic cases and many mild cases that are indistinguishable from the cold or flu, experts have long suspected Covid-19 is more widespread than we know. At the same time, the fatality rate is affected by both undercounts and overcounts

The most up-to-date estimate by the Oxford Center for Evidence-Based Medicine suspects the death rate is a flu-like 0.1% to 0.39%.

• Herd immunity. Levels of honesty vary, but a fair approximation is that most countries expect the initial epidemic to burn itself out before a vaccine is available

• Value proposition. Getting back to the death rate, the average risk for each of us may be small but when an entire population is subjected to the same newly emergent small risk at the same time, it can overwhelm emergency rooms

The panicked governmental responses and clampdowns we’ve seen are best understood in this vein: A very low risk of death for a very large number of people has created a global crisis.

Not helping is the reality described in detail by the world’s newspapers: Recovery of the most severely affected patients on ventilators is rare and involves a great deal of personal suffering.

The president, though, was slow to absorb the scale of the risk and to act accordingly, focusing instead on controlling the message, protecting gains in the economy and batting away warnings from senior officials.

Mr. Trump’s response was colored by his suspicion of and disdain for what he viewed as the “Deep State” — the very people in his government whose expertise and long experience might have guided him more quickly toward steps that would slow the virus, and likely save lives.

The slow start of that plan, on top of the well-documented failures to develop the nation’s testing capacity, left administration officials with almost no insight into how rapidly the virus was spreading. “We were flying the plane with no instruments,” one official said.

But dozens of interviews with current and former officials and a review of emails and other records revealed many previously unreported details and a fuller picture of the roots and extent of his halting response as the deadly virus spread:

The National Security Council office responsible for tracking pandemics received intelligence reports in early January predicting the spread of the virus to the United States, and within weeks was raising options like keeping Americans home from work and shutting down cities the size of Chicago. Mr. Trump would avoid such steps until March.

Despite Mr. Trump’s denial weeks later, he was told at the time about a Jan. 29 memo produced by his trade adviser, Peter Navarro, laying out in striking detail the potential risks of a coronavirus pandemic: as many as half a million deaths and trillions of dollars in economic losses.

The health and human services secretary, Alex M. Azar II, directly warned Mr. Trump of the possibility of a pandemic during a call on Jan. 30, the second warning he delivered to the president about the virus in two weeks. The president, who was on Air Force One while traveling for appearances in the Midwest, responded that Mr. Azar was being alarmist

Mr. Azar publicly announced in February that the government was establishing a “surveillance” system

the task force had gathered for a tabletop exercise — a real-time version of a full-scale war gaming of a flu pandemic the administration had run the previous year. That earlier exercise, also conducted by Mr. Kadlec and called “Crimson Contagion,” predicted 110 million infections, 7.7 million hospitalizations and 586,000 deaths following a hypothetical outbreak that started in China.

By the third week in February, the administration’s top public health experts concluded they should recommend to Mr. Trump a new approach that would include warning the American people of the risks and urging steps like social distancing and staying home from work.

But the White House focused instead on messaging and crucial additional weeks went by before their views were reluctantly accepted by the president — time when the virus spread largely unimpeded.

When Mr. Trump finally agreed in mid-March to recommend social distancing across the country, effectively bringing much of the economy to a halt, he seemed shellshocked and deflated to some of his closest associates. One described him as “subdued” and “baffled” by how the crisis had played out. An economy that he had wagered his re-election on was suddenly in shambles.

He only regained his swagger, the associate said, from conducting his daily White House briefings, at which he often seeks to rewrite the history of the past several months. He declared at one point that he “felt it was a pandemic long before it was called a pandemic,” and insisted at another that he had to be a “cheerleader for the country,” as if that explained why he failed to prepare the public for what was coming.

Mr. Trump’s allies and some administration officials say the criticism has been unfair.

The Chinese government misled other governments, they say. And they insist that the president was either not getting proper information, or the people around him weren’t conveying the urgency of the threat. In some cases, they argue, the specific officials he was hearing from had been discredited in his eyes, but once the right information got to him through other channels, he made the right calls.

“While the media and Democrats refused to seriously acknowledge this virus in January and February, President Trump took bold action to protect Americans and unleash the full power of the federal government to curb the spread of the virus, expand testing capacities and expedite vaccine development even when we had no true idea the level of transmission or asymptomatic spread,” said Judd Deere, a White House spokesman.

Decision-making was also complicated by a long-running dispute inside the administration over how to deal with China

The Containment IllusionBy the last week of February, it was clear to the administration’s public health team that schools and businesses in hot spots would have to close. But in the turbulence of the Trump White House, it took three more weeks to persuade the president that failure to act quickly to control the spread of the virus would have dire consequences.

There were key turning points along the way, opportunities for Mr. Trump to get ahead of the virus rather than just chase it. There were internal debates that presented him with stark choices, and moments when he could have chosen to ask deeper questions and learn more. How he handled them may shape his re-election campaign. They will certainly shape his legacy.

Facing the likelihood of a real pandemic, the group needed to decide when to abandon “containment” — the effort to keep the virus outside the U.S. and to isolate anyone who gets infected — and embrace “mitigation” to thwart the spread of the virus inside the country until a vaccine becomes available.

Among the questions on the agenda, which was reviewed by The New York Times, was when the department’s secretary, Mr. Azar, should recommend that Mr. Trump take textbook mitigation measures “such as school dismissals and cancellations of mass gatherings,” which had been identified as the next appropriate step in a Bush-era pandemic plan.

The group — including Dr. Anthony S. Fauci of the National Institutes of Health; Dr. Robert R. Redfield of the Centers for Disease Control and Prevention, and Mr. Azar, who at that stage was leading the White House Task Force — concluded they would soon need to move toward aggressive social distancing