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Top health officials are quarantining after being exposed.

In the latest sign of worry that the coronavirus could be spreading through the senior ranks of the Trump administration, three top public health officials have begun partial or full self-quarantine for two weeks after coming into contact with someone who has tested positive for the coronavirus.

Representatives for Dr. Robert Redfield, the director of the Centers for Disease Control and Prevention, and Dr. Stephen Hahn, the commissioner of the Food and Drug Administration, confirmed the precautions on Saturday. Dr. Anthony S. Fauci, the director of the National Institute of Allergy and Infectious Diseases, confirmed a CNN report that he had begun a “modified quarantine” given what he called a “low risk” contact.

The actions come after the disclosure on Friday that Vice President Mike Pence’s press secretary, Katie Miller, tested positive for the virus. Ms. Miller has attended numerous meetings of the White House’s coronavirus task force, which also includes Dr. Redfield, Dr. Hahn and Dr. Fauci.

Dr. Fauci will telework from home and wear a mask for 14 days, he told CNN, possibly visiting his office at the National Institutes of Health when he will be the only person present. He tested negative for the virus on Friday and plans to be tested daily from now on.

Dr. Redfield also had a “low-risk exposure” with a person at the White House, on May 6, and will be teleworking for the next two weeks, Benjamin Haynes, a C.D.C. spokesman, said in a statement. Dr. Redfield “is feeling fine, and has no symptoms,” he said, adding that if Dr. Redfield needed to visit the White House for official business he would follow C.D.C. safety guidelines for essential workers who may have been exposed to the virus. Those guidelines call for temperature checks, screening for symptoms, masks as well as social distancing.

A spokeswoman for the F.D.A. said that Dr. Hahn had sent a note to his staff on Friday disclosing his contact with a person who had tested positive for Covid-19 and that, in accordance with C.D.C. guidelines, “is now in self-quarantine for the next two weeks.”

“Dr. Hahn immediately took a diagnostic test and tested negative for the virus,” added the spokeswoman, Stephanie Caccomo.

She and Mr. Haynes did not identify the person or people to whom Dr. Redfield and Dr. Hahn had been exposed, although the C.D.C. statement indicated that it was a person “at the White House.” The CNN report confirmed by Dr. Fauci said that his contact of concern was with a White House staff member.

The White House said this week that a military valet to President Trump had also tested positive for the virus.

Senator Lamar Alexander, Republican of Tennessee, who oversees the Senate’s health committee, said in a statement Saturday that the White House had agreed to give Dr. Hahn and Dr. Redfield a “one-time exception” and allow them to testify by videoconference at a scheduled hearing on Tuesday about how to return safely to work and school.

Tracking the high coronavirus toll in U.S. nursing homes.

At least 25,600 residents and workers have died from the coronavirus at nursing homes and other long-term care facilities for older adults in the United States, according to a New York Times database.

While just about 10 percent of the country’s cases have occurred in long-term care facilities, deaths related to Covid-19 in these facilities account for a third of the country’s pandemic fatalities. And in about a dozen states, including Maryland, Oregon and Colorado, such facilities account for an even larger segment — more than half — of deaths.

In the absence of comprehensive data from some states and the federal government, The Times has been assembling its own database of coronavirus cases and deaths at these facilities.

The findings are laid out, and explained, in a series of charts and graphics. The data can also be searched for locations of named facilities with at least 50 recorded cases.

Nursing home populations are at a high risk of being infected by — and dying from — the coronavirus, according to the Centers for Disease Control and Prevention. Covid-19, the disease caused by the coronavirus, is known to be particularly lethal to older adults with underlying health conditions, and can spread more easily through congregate facilities, where many people live in a confined environment and workers move from room to room.

Information from the states themselves about such facilities has been a mix: About a dozen states report very little or nothing at all. Some states, including Colorado, Illinois, Maryland, Nevada, New Jersey and South Carolina, regularly release cumulative data on cases and deaths at specific facilities. California, Massachusetts, Michigan and Ohio, among others, provide some details on the number of cases — but not on deaths. Others report aggregate totals for their state but provide no information on where the infections or deaths have occurred.

Trump is losing ground with seniors when it comes to his handling of the virus.

The coronavirus and the Trump administration’s response to it have cost President Trump support from one of his most crucial constituencies: America’s seniors.

For years, Republicans and Mr. Trump have relied on older Americans, the United States’ largest voting bloc, to offset Democrats’ advantage with younger voters. But seniors are also the most vulnerable to the coronavirus, and the Trump campaign’s internal polls show his support among voters over age 65 softening to a concerning degree, people familiar with the numbers said.

A recent Morning Consult poll found that Mr. Trump’s approval rating on the handling of the coronavirus was lower with seniors than with any other group other than young voters. And Vice President Joseph R. Biden Jr., the presumptive Democratic nominee, in recent polls held a 10-point advantage among voters who are 65 and older. A poll commissioned by the campaign showed a similar double-digit gap.

As that has taken shape, the president has all but moved on from a focus on controlling the pandemic and is pushing his agenda to restore the country to a place that will lift his campaign. That has included making clear that despite the pandemic, he wants a traditional political convention in Charlotte, N.C., in late August, with thousands of sign-waving Republican delegates from out of state filling an arena.

But in North Carolina, state officials are not so sure. Even the Republicans.

“I think it’s very clear it may not be possible to host a convention as planned,” said Edmund H. Driggs, a Republican member of the Charlotte City Council.

And the debate is taking place as elements of the pandemic — including its death toll in the United States — have become heated campaign flash points as some voters turn scientific questions into political issues.

“It’s, ‘I don’t like what this implies; therefore I’m going to deny the evidence, and I’m going to question the models, and I’m going to question the motivations of the people who do it,”’ said Naomi Oreskes, a science historian at Harvard.

A virus ‘conspiracy’ video has gone viral.

In a video posted to YouTube on Monday, a woman animatedly described an unsubstantiated secret plot by global elites like Bill Gates and Dr. Anthony Fauci to use the coronavirus pandemic to profit and grab political power.

In the 26-minute video, the woman asserted how Dr. Fauci, the director of the National Institute of Allergy and Infectious Diseases and a leading voice on the coronavirus, had buried her research about how vaccines can damage people’s immune systems. It is those weakened immune systems, she declared, that have made people susceptible to illnesses like Covid-19.

The video, a scene from a longer dubious documentary called “Plandemic,” was quickly seized upon by anti-vaccinators, the conspiracy group QAnon and activists from the Reopen America movement, generating more than eight million views. And it has turned the woman — Dr. Judy Mikovits, 62, a discredited scientist — into a new star of virus disinformation.

Her ascent was powered not only by the YouTube video but also by a book that she published in April, “Plague of Corruption,” which frames Dr. Mikovits as a truth-teller fighting deception in science. In recent weeks, she has become a darling of far-right publications like The Epoch Times and The Gateway Pundit. Mentions of her on social media and television have spiked to as high as 14,000 a day, according to the media insights company Zignal Labs.

The F.D.A. approves the first antigen test for detecting the virus.

The Food and Drug Administration has approved the first antigen test that can rapidly detect whether a person has been infected by the coronavirus, a significant advancement that promises to greatly expand the nation’s testing capacity.

The test, by the Quidel Corporation of San Diego, was given emergency use authorization late Friday by the F.D.A., according to a notice on the agency’s website.

Unlike commonly available coronavirus tests that use polymerase chain reaction, or PCR, antigen diagnostics work by quickly detecting fragments of virus in a sample. The newly approved Quidel test will rely on specimens collected from nasal swabs, according to the F.D.A., and they can only be processed by the company’s lab instruments.

“Diagnostic testing is one of the pillars of our nation’s response to Covid-19, and the F.D.A. continues to take actions to help make these critical products available,” the agency said in a statement on Saturday. “One of the main advantages of an antigen test is the speed of the test, which can provide results in minutes.” The F.D.A. said it expected to grant emergency clearance for other antigen tests in the near future.

Experts said the approval of an antigen test for Covid-19 would bolster testing efforts by giving medical workers and health authorities an inexpensive tool for mass rapid testing. Further developed, antigen tests also hold potential for use at home, in the manner of a home pregnancy kit.

“I am very enthusiastic about antigen testing because of its ability to be scaled up to millions of tests a day, and because it has a much more rapid turnaround,” said Dr. Ashish Jha, director of the Harvard Global Health Institute. “A lot of us have been looking forward to this moment.”

A California prison has one of the nation’s largest clusters of cases.

At least 850 inmates and 11 staff members at a federal prison in California have tested positive for the coronavirus, the largest outbreak in the federal prison system, according to federal data.

More than 70 percent of the 1,162 inmates at Federal Correctional Institution Lompoc in Santa Barbara County have contracted the virus, according to data from the Bureau of Prisons, underscoring how the pandemic continues to sweep through prisons and jails, where social distancing is nearly impossible and conditions are often unsanitary.

In an effort to control the spread of the virus, F.C.I. Lompoc has suspended all prison visits and has barred inmates from using telephones and email stations until May 18. The restrictions have prompted protests from the families of some inmates.

“People are dying, and we don’t know how our family is in there,” Alexandria Estrada of Tucson, Ariz., whose relative is incarcerated at Lompoc, told The Lompoc Record last month. “They won’t tell us.”

The Bureau of Prisons said that it recently began testing the entire inmate population at F.C.I. Lompoc and had turned the gym, chapel, visiting room and other areas into inmate housing to increase social distancing.

Prison officials said they had also converted a former factory inside the prison into a hospital unit for virus patients, and were encouraging family members to stay in touch with inmates by mail.

“The institution recognizes how important it is to maintain family contact during these uncertain times,” the bureau said in a statement on Saturday.

F.C.I. Lompoc has the ninth-largest known cluster of coronavirus cases in the United States, and the sixth-largest cluster inside a correctional facility, according to a New York Times analysis. State prisons in Ohio, Tennessee and Arkansas have more known cases, as does the county jail in Chicago.

As the U.S. eyes reopening, South Korea provides a cautionary tale.

With more than half of the states moving to ease restrictions that allow people to return to work and some parts of public life, leaders across the United States are cautiously hoping that the pace of the virus’s spread has slowed enough to make a limited reopening manageable.

But a recent cluster of cases in South Korea that led the mayor of Seoul to indefinitely close down bars and nightclubs on Saturday demonstrated how precarious that process can be, even as new infection rates are declining.

South Korea’s early and aggressive response to the arrival of the virus in March helped turn the country’s experience into a success story, significantly flattening the curve of new infections and preventing a full-blown outbreak in one of the world’s more densely populated countries. Experts attributed the success to early widespread testing, contact tracing, isolation measures and public will. The progress was so encouraging that the country moved ahead with reopening businesses and schools and approving sporting events.

Yet even as South Korea has come close to stamping out the virus, bringing infections down to around 10 cases per day in recent weeks, its capital now has at least 27 new cases connected to a single patient who may have spread the virus around several nightclubs.

In the United States, which records nearly 25,000 new cases a day, many experts have warned that reopening while the country is near the peak of the outbreak’s curve could have dire consequences, with new clusters popping up in far-flung and unexpected corners.

Ultimate Fighting becomes the first major U.S. sport to emerge from a shutdown.

On Saturday night, in a nearly empty arena in Jacksonville, Fla., an event by the world’s biggest mixed martial arts organization became the first major North American sport to return from an industrywide shutdown amid the pandemic.

The organization, the Ultimate Fighting Championship, also plans to stage two more cards in Jacksonville next week. And with no competition from Major League Baseball or from hockey and basketball playoffs, U.F.C. is positioned for a big viewership win.

Yet its success will also be measured by whether it proves harmful to public health. On Friday night, U.F.C. officials said that one of their fighters, Ronaldo Souza, a Brazilian middleweight nicknamed Jacare, had been pulled from Saturday’s event because he had tested positive for the coronavirus earlier in the day. The U.F.C. said in a statement that two of Souza’s cornermen had also tested positive for the virus.

States reopen in different stages, in an economic and public health experiment.

States that are taking steps to reopen in the next week will serve as laboratories for the hoped-for economic recovery in the face of a pandemic that has touched nearly every aspect of American life.

Gov. Gavin Newsom of California announced on Friday that a range of retailers like bookstores and florists could resume selling via curbside pickup. But in an acknowledgment by state officials that the outbreak is unlikely to subside by the fall, the governor ordered mail-in ballots to be sent to the state’s 20.6 million voters for the November election.

Michigan cautiously enacted plans to allow construction and factory workers to return to work sites. Pennsylvania and North Carolina on Friday also allowed some retailers to open, though with certain restrictions like limits on the number of customers allowed inside shops.

Gov. Steve Sisolak of Nevada said that restaurants and personal care businesses could start to reopen on Saturday, but residents were encouraged to stay home, and bars and casinos remained closed. In Ohio, Gov. Mike DeWine’s reopening plan, which he outlined last month, began with certain industries in early May and is set to accelerate with retail stores starting on Tuesday. But Mr. DeWine said other businesses — including restaurants and salons — would have to wait. “We are not quite there yet,” he said.

Job losses have encompassed the entire economy, affecting every major industry. Areas like leisure and hospitality had the biggest losses in April, but even health care shed more than a million jobs. Low-wage workers, including many women and members of racial and ethnic minorities, have been hit especially hard.

“It’s literally off the charts,” said Michelle Meyer, head of U.S. economics at Bank of America. “What would typically take months or quarters to play out in a recession happened in a matter of weeks this time.”

Three children have died of a mysterious syndrome linked to the virus.

Three young children have died in New York of a mysterious toxic-shock inflammation syndrome with links to the coronavirus, Gov. Andrew M. Cuomo said on Saturday.

As of Saturday, more than 73 children in New York have been sickened by the rare illness, which has some similarities similar to Kawasaki disease. Mr. Cuomo said many of these children did not show respiratory symptoms commonly associated with the coronavirus when they were brought to area hospitals, but all of them tested positive either for Covid-19 or for its antibodies.

When the coronavirus pandemic began ravaging the New York area two months ago, the state found solace in the initial evidence that children would be largely unaffected, Mr. Cuomo said. That sense of relief was shattered this week when a 5-year-old died in New York City of the newly discovered disease, which doctors described as a “pediatric multisystem inflammatory syndrome.”

Mr. Cuomo did not elaborate on the death of the two additional children, but has asked parents to be vigilant in looking for symptoms such as prolonged fever, severe abdominal pain, change in skin color, racing heart and chest pain.

Before the announcement of the deaths attributed to the new illness, only three children had died of the virus in New York, according to the most recent breakdown from the state.

Mr. Cuomo said the state was working with the Centers for Disease Control and Prevention to determine whether the confounding illness had been affecting children infected with the virus before this week.

“It is very possible that this has been going on for several weeks and it hasn’t been diagnosed as related to Covid,” Mr. Cuomo said.

Sioux tribal leaders rebuff governor’s request to remove checkpoints.

Sioux tribal leaders have rejected a request from Gov. Kristi Noem of South Dakota to remove travel checkpoints they established on state and federal highways, saying they were necessary to stop the spread of the virus on tribal land.

In letters on Friday to the Oglala Sioux Tribe and the Cheyenne River Sioux Tribe, Ms. Noem threatened legal action if they did not remove the checkpoints in 48 hours.

The episode underscores the particular challenges facing hard-hit tribal nations as they seek to respond to the pandemic. Already, tribes across the country struggle with inadequate federal resources and are among the most vulnerable to the virus. Last month, a group of tribes sued the Treasury Department over who was eligible for stimulus relief money, and the agency said this week that it would begin distributing $ 8 billion in aid to tribal governments.

As the coronavirus took hold in South Dakota, Ms. Noem did not issue a stay-at-home order for the state, and announced guidelines for businesses to reopen if there had been a downward trend in known cases in the surrounding area for 14 days.

In a tweet on Friday, she wrote that the tribes should work with the state in the fight against the virus, “not against their fellow South Dakotans.”

The chairman of the Cheyenne River Sioux Tribe, Harold Fraizer, said that while he agreed South Dakotans needed to work together, the governor was interfering “in our efforts to do what science and facts dictate.”

“The virus does not differentiate between members and nonmembers,” he said in a statement. “It obligates us to protect everyone on the reservation regardless of political distinctions.”

Federal officials ship remdesivir to hard-hit states after an outcry from doctors.

The federal government said on Saturday that it was distributing thousands of vials of the antiviral drug remdesivir to state health departments after an outcry from doctors across the country who said they had been denied access to the only approved therapy for hospitalized coronavirus patients.

The announcement was prompted by a backlash from doctors who questioned an opaque distribution system that appeared to favor some hospitals that had few coronavirus patients while skipping over the most besieged. For example, Massachusetts General, a Harvard University teaching hospital, received cases of the drug though officials there said they had not asked for it. Yet other major hospitals were left out, including Boston Medical Center, which has many vulnerable African-American patients.

In response, the Department of Health and Human Services said that it had begun to ship 360 cases of the drug to six states that have been hard hit by the pandemic: Connecticut, Illinois, Iowa, Maryland, Michigan and New Jersey. Each case contains 40 vials.

The agency said that Gilead Sciences, the maker of remdesivir, had donated the experimental drug, which earlier this month was given emergency approval by the Food and Drug Administration for the treatment of patients severely ill with Covid-19, the disease caused by the coronavirus. Clinical trials have found that individuals who received remdesivir recovered faster than those who were given a placebo, in 11 days, versus 15 days. But the drug did not significantly reduce fatality rates, the studies found.

“State health departments will distribute the doses to appropriate hospitals in their states because state and local health departments have the greatest insight into community-level needs in the Covid-19 response,” the agency said in a statement.

The drug had previously been dispensed by a wholesale distributor, AmerisourceBergen, according to a list drawn by the federal government.

Friends got back together to buy a tulip farm — but then the virus arrived.

Five friends who had gone to high school in Mount Vernon, Wash., together decades ago thought they had a great plan to get the gang together again.

“We went out to a happy hour and ended up buying a farm,” said Angela Speer, one of the friends who decided to buy Tulip Town, the 30-acre site, last summer.

Their timing was terrible.

The stay-at-home orders in Washington State this spring meant that their expected small window for making profits was slammed shut. The annual tulip festival that draws crowds north of Seattle to Skagit County, where three-quarters of the nation’s commercial tulip crop is grown, was canceled.

The five newcomers on their small farm realized something: Coming in new meant that everything about the way the tulip business was supposed to work was also new, to be tried and tested — and possibly reinvented.

America must decide which spending to emphasize: federal or personal.

As the United States confronts unemployment levels not seen since the Great Depression, Congress and the Trump administration face a pivotal choice: Continue spending trillions trying to shore up businesses and workers, or bet that state reopenings will jump-start the U.S. economy.

At least 20 million people in America are unemployed, and a large share of the nation’s small businesses are shut and facing possible insolvency. Policy misjudgments in the coming weeks could turn the 18 million temporary layoffs recorded in April into permanent job losses that could plunge the United States into a deep and protracted recession unrivaled in recent history.

Yet the federal government is lurching away from the strategy that has thus far helped slow the spread of the coronavirus and sustain people and companies struggling during the economic shutdown.

Over the past two months, as consumers and workers retreated and state officials imposed limits on economic activity, President Trump and bipartisan coalitions in the House and Senate have approved $ 3 trillion in federal spending to help companies, workers and the unemployed. The Federal Reserve has taken extraordinary steps to keep the financial system functioning, buying up government-backed securities and embarking on plans to purchase corporate and municipal debt to keep credit flowing. Governors have embraced stay-at-home orders in an effort to slow the virus’s spread.

But as the virus threatens to haunt the nation and its economy longer than some officials had anticipated, Mr. Trump and many Republicans in Congress have grown weary of federal spending to support workers and businesses and have begun urging states to get back to what was considered normal.

Economists, including liberals and many conservatives, warn that ending efforts to aid businesses and workers without first enacting a new strategy could force the economy into a summer of partial recoveries, rising infection rates and insufficient support for struggling businesses and those out of work.

The pandemic has widened longstanding educational gaps.

A close look at two very different first-grade classes in two of America’s largest cities, Chicago and Philadelphia, shows how the crisis has laid bare the discrepancies between some private schools, which can provide luxury learning online, and many public schools, which are struggling to adjust.

The pandemic has made it clear that online education requires a mix of elements that not all schools can provide: enthusiastic leadership, teacher expertise and homes equipped with everything children need to learn effectively.

At Chicago Jewish Day School, Rachel Warach helps give her first-grade students four hours and 15 minutes of daily live instruction, including yoga, art and music. Students who need extra help can be assisted remotely with a tutor or a social worker. The school has sent home supplies, and parents have provided internet access, computers and quiet study areas.

At Spruance Elementary in Philadelphia, in one first-grade class, only about 11 of 26 students attend daily.

Dolores Morris, a first-grade teacher there, meets with her students each morning for just an hour. Despite being near retirement, she has thrown herself into learning the technology to teach remotely. Often, she exchanges messages with parents while interacting with her students via Google Classroom.

“I’m thanking God that I can at least see their faces,” she said.

Doctors and patients alike suffer as elective procedures are put on hold.

The shutdown of elective surgeries and other “nonessential” medical care by federal and state officials during the pandemic has left the nation’s 5,200 hospitals, particularly in places where there have been relatively few infections, with idle clinics, vacant operating rooms and a dearth of patients.

“Our hospitals, like every other hospital in the country, are half empty,” said Marvin O’Quinn, the president and chief operating officer for CommonSpirit Health, a Catholic system that operates 137 hospitals across 21 states.

A report released by the Centers for Disease Control and Prevention on Friday revealed a huge decline in standard childhood vaccinations during March and April as pediatric offices canceled orders for millions of doses of vaccine for diseases such as measles. Other routine visits for dental checkups and physical therapy have seen similar declines.

More alarmingly, even hospital visits for much more serious conditions like heart attacks and appendicitis appear to be down drastically as patients weigh the risks of entering emergency rooms.

As restrictions ease around the country, some states have begun allowing procedures unrelated to the coronavirus, like knee replacements, colonoscopies and mammogram screenings. But after nearly two months of national action to slow the virus’s spread, the interruption of many medical procedures generally has affected patients with a variety of conditions who suddenly have no choice but to delay nonemergency procedures and preventive care.

Doctors and other medical experts join the front-lines on ballots, too.

In 2018, the United States experienced a “STEM wave” of scientists running for office, and Congress welcomed nine new members with degrees in science, technology, engineering and medicine — two Republicans and seven Democrats. Five were women.

Some candidates said they had decided to enter a new arena because they viewed the Trump administration as hostile to their old one: scientific expertise. A president who said there are “scientists on both sides of the issue” on climate change was cause for alarm.

For some, that alarm has grown in light of the government’s response to the coronavirus outbreak. The coronavirus has given front-line physicians a clear view of the life-or-death stakes of government decision making, whether on social distancing or contact tracing.

And as the pandemic turns a spotlight on health care workers, many doctors-turned-candidates say it’s time to try to convert those cheers into votes.

“Part of what people are looking for is not the status quo,” said Shaughnessy Naughton, a chemist who is president of 314 Action, a political action committee that aims to see more scientists in politics. “Women and physicians represent change.”

The latest from our correspondents around the world.

Reporting was contributed by Reed Abelson, Davey Alba, Alexandra Alter, Nicholas Bogel-Burroughs, Morgan Campbell, Emily Cochrane, Michael Crowley, Sheera Frenkel, Trip Gabriel, Emma Goldberg, Dana Goldstein, Maggie Haberman, C.J. Hughes, Danielle Ivory, Andrew Jacobs, Kirk Johnson, Annie Karni, K.K. Rebecca Lai, Michael Levenson, Zach Montague, Kwame Opam, Matthew Rosenberg, Jim Rutenberg, Choe Sang-Hun, Mitch Smith, Nicole Sperling, Jim Tankersley, Michael Wilson and Karen Yourish.