Coronavirus Live Updates: Trump Administration Gives Formal Notice That U.S. Will Leave the W.H.O. Next Year


President Jair Bolsonaro of Brazil, who had been a skeptic of antivirus precautions, tested positive. City halls across the U.S. are finding ways to reopen.

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Ohio’s governor issued an order requiring residents to wear masks in public in seven counties that are seeing serious growth in cases, including the counties that contain Columbus, Cincinnati and Cleveland.

ImagePresident Trump in Keystone, S.D. last week.
President Trump in Keystone, S.D. last week.Credit...Anna Moneymaker for The New York Times

The Trump administration has formally notified the United Nations that the United States is withdrawing from the World Health Organization, officials said Tuesday, cutting off one of the organization’s biggest sources of aid amid a global pandemic that has infected more than 11.6 million people, killed more than a half a million, and upended life around the world.

“The United States’ notice of withdrawal, effective July 6, 2021, has been submitted to the UN Secretary-General, who is the depository for the W.H.O.,” said a senior administration official.

By law the United States must give the organization a year’s notice if it intends to withdraw, and meet all the current financial obligations in the current year.

Mr. Trump, whose response to the pandemic has drawn criticism, first announced that he planned to halt funding to the W.H.O. in April, claiming that the organization had made a series of mistakes as it battled the virus. The biennial budget for the W.H.O. is about $6 billion, which comes from member countries around the world. In 2019, the last year for which figures were available, the United States contributed about $553 million.

His move drew immediate criticism, including from Senator Bob Menendez of New Jersey, who wrote on Twitter that Congress had just received notification of the withdrawal. “This won’t protect American lives or interests — it leaves Americans sick & America alone,” he wrote.

The president of the United Nations Foundation, Elizabeth Cousens, said in a statement that the administration’s “move to formally withdraw from W.H.O. amid the greatest public health crisis that Americans and the world have faced in a century is shortsighted, unnecessary, and unequivocally dangerous.”

The W.H.O., founded in 1948, is a postwar creation of the United Nations — and is the world’s premier global health organization. Mr. Trump turned on the organization this spring, accusing it of doing too little to warn the world of the outbreak.

In fact, the agency issued its first alarm on Jan. 4, just five days after the local health department of Wuhan announced a cluster of 27 cases of an unusual pneumonia at a local seafood market, and followed up with a detailed report the next day.

Lawrence Gostin, the director of the W.H.O.’s Collaborating Center on National & Global Health Law, called the decision “among the most ruinous presidential decisions in recent history.”

“It will make Americans less safe during an unprecedented global health crisis,” he said. “And it will significantly weaken U.S. influence on W.H.O. reform and international health diplomacy. This disastrous action is deeply damaging to U.S. national interests.”

Experts acknowledged that the W.H.O. has made some missteps during the pandemic, but said that it has largely done well given the constraints under which it operates. The agency is coordinating clinical trials of treatments, as well as efforts to manufacture and equitably distribute the vaccine worldwide.

Dr. Ashish Jha, director of the Harvard Global Health Institute, said that the administration’s move to withdraw “will both harm global public health and harm the health of the American people.”

Brazil’s president, Jair Bolsonaro, tests positive. He has been a skeptic of antivirus precautions.

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President Jair Bolsonaro of Brazil has repeatedly dismissed the danger posed by the coronavirus. On Tuesday, he disclosed that he had the virus.

President Jair Bolsonaro of Brazil, who has repeatedly dismissed the danger posed by the virus, disclosed Tuesday that he has the virus, a development that turbocharged the debate over his cavalier handling of a pandemic that has killed more than 65,000 Brazilians.

Speaking to journalists shortly after noon on Tuesday, the president, 65, said he was tested after experiencing fatigue, muscle pain and a fever.

Mr. Bolsonaro said he was feeling well on Tuesday, which he credited to having taken hydroxychloroquine, an anti-malaria pill repeatedly promoted by Mr. Trump that has not been proven as a treatment for Covid-19 patients.

“I’m fine, I’m very well,” Mr. Bolsonaro said, standing a few feet away from journalists.

Mr. Bolsonaro has come under criticism for his handling of the pandemic, even as Brazil’s caseload and death toll ballooned in recent months. Brazil’s 1.6 million diagnosed cases make it the second hardest-hit country, trailing only the United States.

Though several of his aides have tested positive in recent months, the president has often eschewed precautions such as wearing a mask and practicing social distancing. Most recently, he attended a luncheon hosted on Saturday by the American ambassador in Brazil to celebrate the Fourth of July holiday.

A photo taken during the lunch and posted on Twitter by Foreign Minister Ernesto Araújo shows the president sitting next to the American ambassador, Todd Chapman, giving a thumbs-up sign at a table decorated with an American flag design. The American embassy said on Tuesday that Mr. Chapman had tested negative, but would remain in isolation.

Mr. Bolsonaro is one of a number of world leaders who have contracted the virus.

Prime Minister Boris Johnson of Britain, who was also criticized for seeming to dismiss the risks of the virus early on, tested positive in March and spent three nights in intensive care. President Juan Orlando Hernández of Honduras was released from the hospital on Thursday after spending more than two weeks being treated for Covid-19 and related pneumonia. Prime Minister Mikhail Mishustin of Russia said he tested positive in April, and Prime Minister Nikol Pashinyan of Armenia said that he and his family tested positive in June.

A motorcyclist passed graffiti critically depicting President Jair Bolsonaro of Brazil in Rio de Janeiro on Tuesday.Credit...Dado Galdieri for The New York Times

As Brazilians awaited the results of the president’s latest virus test, messages posted on social media illustrated how polarized the country had become. Two trending hashtags on Twitter Tuesday morning were #ForçaBolsonaro and #ForçaCorona, the first sending the president strength and the other effectively expressing hope that the president falls ill.

Harvard in May. Many top universities have large numbers of international students who will be affected by the new immigration rule.Credit...Cassandra Klos for The New York Times

Immigration authorities announced Monday that they would discontinue exceptions to visa requirements that are currently allowing international students studying at American universities to attend all of their classes online.

As a result of the change in policy, foreign students whose college campuses will not reopen for the fall semester will be required to return to their home countries, as their visas will no longer be considered valid.

More than a million international students were issued visas to study in the United States last year. This spring, as the pandemic prompted most American college campuses to close, some universities, including Ivy League schools, rushed students onto planes to their home countries.

Some students tried to hang on to their educations by couch surfing in the homes of peers and relying on donated food and grants to keep up with their tuition payments, and many lost their on-campus jobs. International students were not eligible for federal aid funds tied to the pandemic.

Early in the outbreak, American immigration authorities announced they would make exceptions to the requirements of international student visas, allowing the students to take classes online rather than in person — a change that is now being partially reversed. The news that international students must now attend at least some of their classes in person in order to hold onto their legal immigration status will likely, for many, end the prospects of completing their educational goals.

As cases rise, some Florida hospitals are running out of intensive care beds.

A line of cars at a testing site on Tuesday in Miami Beach.Credit...Saul Martinez for The New York Times

As cases surge in Florida, more than 40 hospitals in counties across the state reported having no more beds available in their adult intensive care units, according to the state’s health care administration website.

Gov. Ron DeSantis, who pushed to reopen the state swiftly, announced Tuesday that he was taking steps to augment hospital capacity. The state has reported at least 213,786 cases, according to a New York Times database, and at least 3,840 people there have died. The average number of new cases in Florida each day has doubled since late June. On Tuesday, the state added more than 7,300 new cases.

Mr. DeSantis said the state would help create another nursing home for people with the virus, and would send 100 health care workers, mostly nurses, to Miami-Dade County’s public hospital network, Jackson Health System. Some patients seeking medical care for other problems were testing positive, he said, putting a strain on space and staffing as hospitals were forced to isolate them.

“We have abundant capacity, but I think that having some of the personnel support will be very very important,” the governor said.

Miami-Dade County has been hit particularly hard. Its mayor, Carlos A. Gimenez, said that the county’s positivity rate had risen above 20 percent, more than double what it was two weeks ago. And nearly 80 percent of its I.C.U. beds are filled with virus patients, the county reported.

Mr. Gimenez has sent conflicting messages in recent days about some of the steps he was taking to curb the spread in the Miami area. After announcing on Monday that he would close gyms and restaurants, except for takeout and delivery, he later amended his decision and said that he would allow outdoor dining at tables with no more than four people. On Tuesday, he added that he had reached a compromise to allow gyms to stay open as long as people wear masks.

Months into the pandemic, many U.S. cities still lack testing capacity.

A coronavirus test site in Phoenix last week. In Arizona, where cases have grown to more than 100,000, a shortage of testing has alarmed local officials.Credit...Adriana Zehbrauskas for The New York Times

In the early months of the outbreak in the United States, testing posed a significant problem, as supplies fell far short and officials raced to understand how to best handle the virus. Since then, the country has vastly ramped up its testing capability, conducting nearly 15 million tests in June, about three times as many as it had in April.

But in recent weeks, as cases have surged in many states, the demand for testing has soared, surpassing capacity and creating a new testing crisis.

In many cities, officials said a combination of factors was now fueling the problem: a shortage of certain supplies, backlogs at laboratories that process the tests, and skyrocketing growth of the virus as cases climb in almost 40 states.

Fast, widely available testing is crucial to controlling the virus over the long term, experts say, particularly as the country reopens. With a virus that can spread through asymptomatic people, screening large numbers of people is seen as essential to identifying those who are carrying the virus.

As states with major outbreaks struggled to keep up with demand for testing, the Department of Health and Human Services announced on Tuesday a new model of “surge testing” to help particularly hard-hit areas keep up.

At eight temporary sites in three cities — Baton Rouge, La., Edinburg, Texas, and Jacksonville, Fla. — the federal government will offer 15,000 free tests every day, for as many as 12 days. Results will likely be reported within five days, H.H.S. said.

The sites will allow wide access: Anyone over the age of five can be tested, including anyone with symptoms or possible exposure to a confirmed case, or anyone worried about being infected. Those tested do not need to live in the cities with the testing sites.

The effort was a sign of the Trump administration’s new concern about local resources at a time when it has largely handed off responsibility to states. But on a telephone briefing with reporters Tuesday afternoon, Adm. Brett P. Giroir, the assistant secretary for health, said that the new sites were “not to substitute for state testing,” and that there were no plans for the federal government to extend its stays.

“This is really meant to be a targeted intervention,” Admiral Giroir said.

Testing in the United States has not kept pace with other countries, notably in Asia, which have been more aggressive. When there was an outbreak in Wuhan in May, for instance, Chinese officials tested 6.5 million people in a matter of days.

In Arizona, where reported cases have grown to more than 100,000, a shortage of testing has alarmed local officials, who say they feel ill equipped to help residents on their own.

“The United States of America needs a more robust national testing strategy,” Mayor Kate Gallego of Phoenix said in an interview.

Dr. Anthony S. Fauci, the nation’s top infectious disease expert, warned on Monday that the country was still “knee-deep in the first wave” of the pandemic, as the number of coronavirus deaths in the United States passed 130,000 and cases neared three million. Texas and Idaho set daily records for new cases, according to a New York Times database.

A bar in Houston in late June.Credit...Erin Trieb for The New York Times

After hundreds of experts called for the W.H.O. to review its guidance on the possibility of airborne transmission of the virus, the agency acknowledged on Tuesday that airborne transmission may be important in indoor spaces and said it planned to release updated recommendations in a few days.

Agency scientists said at a news briefing that W.H.O. expert committees are reviewing evidence on transmission. But the possibility of airborne transmission in public settings, especially in “crowded, closed, poorly ventilated settings, cannot be ruled out,” said Dr. Benedetta Allegranzi, who leads the W.H.O.’s committee on infection prevention and control.

W.H.O. staff members fielded several questions about transmission of the virus by air, prompted by a widely publicized open letter from 239 experts calling on the agency to review its guidance. Many of the letter’s signatories have collaborated with the W.H.O. and served on its committees.

W.H.O. scientists said that for the past few weeks, the committee has been discussing new evidence on all the ways in which the virus spreads, including by tiny droplets or aerosols.

“We acknowledge that there is emerging evidence in this field as in all other fields,” Dr. Allegranzi said. “And therefore, we believe that we have to be open to this evidence and understand its implications regarding the modes of transmission and also regarding the precautions that need to be taken.”

Agency scientists also offered an explanation for the agency’s seemingly slow pace on revising its recommendations. On average, the scientists review 500 new papers a day, many of which turn out to be of dubious quality. As such, said Dr. Soumya Swaminathan, the W.H.O.’s chief scientist, they have to review the quality of each paper before including it in their analysis.

“Any guidance we put out has implications for billions of people around the world,” she said. “It has to be carefully done.”

At Novavax labs in Rockville, Md., in March.Credit...Andrew Caballero-Reynolds/Agence France-Presse — Getty Images

The deal is the largest that the Trump administration has made so far with a company as part of Operation Warp Speed, the sprawling federal effort to make virus vaccines and treatments available to the American public as quickly as possible. In doing so, the government has placed a significant bet on Novavax, a company based in Maryland that has never brought a product to market.

Operation Warp Speed is a multiagency effort that seeks to carry out Mr. Trump’s pledge to make a coronavirus vaccine available by the end of the year, but the full extent of the project is still unclear. Officials have declined to list which vaccines and treatments are part of Operation Warp Speed.

In an interview on Sunday, Novavax’s president and chief executive, Stanley C. Erck, initially said he was not sure where in the government the $1.6 billion was coming from. A Novavax spokeswoman later said the money was coming from a “collaboration” between the Health and Human Services Department and the Defense Department.

In May, the administration announced it was awarding up to $1.2 billion as part of Operation Warp Speed to the British drugmaker AstraZeneca, which has said that its vaccine could be available by October. Four other companies — Moderna Therapeutics, Johnson & Johnson, Merck and Sanofi — have also received federal assistance for their experimental coronavirus vaccines.

GLOBAL ROUNDUP

Out-of-work Britons fill farm jobs vacant because of travel restrictions.

Harry Penrice at Hall Hunter, where the average weekly pay last year was 414 pounds, or almost $520.Credit...Alex Atack for The New York Times

Fruit picking in Britain is traditionally done by seasonal workers from Eastern Europe. Over all, 70,000 to 90,000 seasonal workers are needed to pick all the fruit and vegetables that grow in the country.

Because of travel restrictions to curb the spread of the coronavirus, many of those workers haven’t been able to make the trip, have been delayed or have chosen not to come. By the time the pandemic hit Europe, most of the crops had been planted.

As a result of the looming labor shortage, the government started a “Pick for Britain” campaign in April to attract British workers. Prince Charles released a video in which he said the country needed “pickers who are stickers.”

Farmers say they have been pleasantly surprised by the amount of interest in these jobs, but the placement of workers has its challenges. Four-fifths of the people who initially expressed interest drop out before moving to the next stage, according to HOPS Labour Solutions. Some realized that manual labor was not for them, or their furlough ended, or the contracts offered by farms were too long.

Still, many are enjoying the work. “It’s been really fun, but it’s been tiring and hard work,” said Ella Chandler, 19, a cricket player whose season was cut short. On a recent day, she said, she picked almost 556 pounds of strawberries. “It’s quite satisfying,” she said.

In other world news:

  • Greece on Monday saw an increase in new infections, reporting 43 new cases, 36 of them foreign arrivals, the highest number in three weeks. Most of Monday’s new cases were tourists from Serbia, prompting the authorities to ban arrivals from the Balkan country until July 15. Greece, which has done relatively well in containing the spread of the virus, opened its regional airports to international travel last Wednesday, keen to salvage what is left of its crucial tourism sector.

  • The virus death toll in India surpassed 20,000 on Tuesday, and, with more than 719,500 confirmed cases, the country has overtaken Russia to become the third hardest-hit, after the United States and Brazil. The country’s public health system is severely strained, and experts believe it may reach a breaking point as Prime Minister Narendra Modi’s government continues to ease a nationwide lockdown.

  • Melbourne, Australia’s second-biggest city, will be locked down for six weeks after a record number of daily coronavirus cases, officials said on Tuesday. The state of Victoria reported 191 new cases on Tuesday, an “unsustainably” high number, said Daniel Andrews, the state’s premier. Most of the cases were in Melbourne, a city of 4.9 million people and the capital of Victoria. Starting late Wednesday night, residents will be allowed to leave their homes only for essential work, shopping and exercise.

  • Prime Minister Boris Johnson of Britain drew furious reactions from health care professionals and opposition lawmakers after he suggested that “too many care homes didn’t really follow the procedures in the way that they could have,” while pleading for better organization and support for the sector. His comments came as coronavirus deaths of nursing home residents in England and Wales approached 20,000, with the figure expected to become much higher.

  • A rule requiring everyone in Toronto to wear face masks or coverings within enclosed public spaces until at least late September was scheduled to take effect on Tuesday. The city is Canada’s largest and has about 15,000 confirmed infections. Masks or face coverings have been mandatory on its public transit network since July 2.

New York Roundup

New York City is considering letting over 3,000 child care centers open next week.

A closed child-care center in Brooklyn in April.Credit...Andrew Seng for The New York Times

New York City’s Board of Health will vote Tuesday on guidelines that, if approved, would allow more than 3,000 child care centers to open next week with new limits.

The rules would allow no more than 15 children in a room, require children and workers to wear face coverings, limit the sharing of toys and allow for frequent disinfection.

At full capacity, 3,000 child care centers can accommodate 150,000 children.

“Folks need to get back to work, and the only way they can do it is with child care,” Mayor Bill de Blasio said at a news conference, adding that “the data consistently shows a low infection rate among children when it comes to the coronavirus.”

The lack of child care options remains one of the biggest obstacles to a wider reopening of New York City, which just eased more restrictions after entering Phase 3 on Monday.

After public schools closed in March, the city opened centers for the children of essential workers. But child care has been limited during the pandemic.

It is still unclear what city schools will look like when they reopen in the fall, but it’s unlikely that children will be in school five days per week. Instead, there are likely to be staggered schedules mixed with remote learning.

Dr. Oxiris Barbot, the city’s health commissioner, said that if child-care centers are allowed to open this Monday, they would meet all state regulations, including daily health screenings and safety plans that include signage for social distancing. The city’s Bureau of Child Care will provide technical assistance to centers that want to open and will also conduct inspections to ensure compliance with the guidelines.

Elsewhere in New York:

  • New York’s governor said the state will require travelers from Delaware, Kansas and Oklahoma to quarantine for 14 days, bringing the list of such states to 19. The governors of New Jersey and Connecticut said they would also instruct travelers from those 19 states to quarantine.

  • Nurses who traveled from across the United States to work in New York City hospitals saw the horrors of the virus up close. Now that many of them have returned home to states in the South and the West, they’re facing a new challenge: persuading friends and family to take it seriously.

  • New York City is mired in its worst economic slump since the financial crisis of the 1970s, when it nearly went bankrupt. The losses have been particularly significant among people of color: About one in four of the city’s Asian, Black and Hispanic workers were unemployed last month, compared with about one of every nine white workers, the city comptroller’s office said.

W.H.O. scientists are headed to China to begin its investigation into how the pandemic began.

Two scientists from the World Health Organization will travel to China this weekend to begin preparations for a larger investigation into the origin of the coronavirus.

The epidemiologist and animal-health specialist will start in Wuhan, where the outbreak began late last year, and will collaborate with experts from the Chinese ministries of science, technology and health. Their purpose is to lay the groundwork for a later investigative expedition.

An international team of scientists has used genetic analysis to trace the likely origin of the novel coronavirus to horseshoe bats; the virus may have spread to humans with help of an intermediate species.

But Dr. Michael Ryan, the executive director of the W.H.O.’s health emergencies program, cautioned it could take years to uncover the source. “The answers to these questions are sometimes elusive,” he said, “and it is quite a detective story to find the source and the intermediate pathways by which the virus breached that barrier to humans.”

While the Chinese government has faced criticism for its response to the outbreak, Dr. Tedros Adhanom Ghebreyesus, the W.H.O.’s director-general, noted that Chinese researchers have also begun to investigate its source. “We should not consider as if there has been no movement or no activity until now,” he said.

The upcoming presidential election could be the most litigious in history.

Processed mail-in ballots at the Bucks County Board of Elections office prior in Doylestown, Pa., in May.Credit...Matt Slocum/Associated Press

The upcoming election is already one of the most divisive in recent history, and it is on track to become the most litigious, as courts weigh policies for voting during a pandemic, voting rights and even who is responsible for paying the return postage used on absentee ballots.

Voting by mail is the prime battleground, with 34 states and the District of Columbia allowing excuse-free absentee voting, most likely ensuring that November’s election in those places will be conducted largely by mail if the pandemic persists.

Many of the remaining states loosened mail-balloting rules for primaries, and some have moved to do so for November as well. But Republicans — led vocally by Mr. Trump — have insisted, without evidence, that loosening absentee ballot rules invites widespread fraud.

Justin Levitt, an election scholar and associate dean at Loyola Law School in Los Angeles, is tracking nearly 130 pandemic-related election lawsuits. The firm of Marc Elias, a lawyer who frequently represents the Democratic Party, is pursuing more than 35 voting rights cases, a number he calls an order of magnitude greater than in the past. And the Republican National Committee, which pledged this spring to spend at least $20 million fighting attempts to loosen voting rules, boasts of filing or intervening in 19 suits to date.

All four of the large U.S. airlines have agreed to terms for loans from the federal government under the March stimulus bill, the Treasury Department said Tuesday.

Delta Air Lines, United Airlines and Southwest Airlines signed letters of intent under that law, known as the CARES Act, Treasury said. Last week, the department announced that American Airlines had agreed to a five-year $4.75 billion loan.

The terms of the loans announced Tuesday have not yet been disclosed, though Delta and United have said that they expect to receive loans nearly as large as American’s. Southwest has said it expects to receive a $1.1 billion loan. In a statement, Southwest said it has only agreed to terms for a loan but has not decided whether it will borrow the money, a decision it will make by Sept. 30.

The CARES Act set aside $25 billion in loans for passenger airlines. The Treasury Department earlier distributed another $25 billion to help the airlines pay workers through September.

Besides the big four airlines, Treasury has also agreed to lend to Alaska Airlines, JetBlue Airways, Frontier Airlines, Hawaiian Airlines, Sky West Airlines and Spirit Airlines.

U.S. ROUNDUP

City halls in the U.S. find ways to reopen.

After months of waiting for a steep drop in cases that never came, many local governments have started reopening their buildings. But the business of assessing properties, paying fines and running America’s cities looks little like it did before the pandemic.

In Aurora, Ill., City Hall was set to open just three days a week, with the first hour each day set aside for older residents. In Detroit’s partly reopened municipal center, appointments were recommended, employees were being tested for the virus and workers were no longer accepting cash payments. And in Dayton, Ohio, where City Hall had been closed since March 18, it was set to reopen this week with hand-sanitizing stations and security guards performing temperature checks.

Even with their front doors unlocked, cities were not exactly encouraging visitors. Officials in Buffalo, who also planned to reopen, said residents with a temperature over 100.4 degrees would not be allowed inside. Detroit officials planned to offer curbside service. Dayton’s news release announcing its reopening included an explicit suggestion to not come:

“The City of Dayton is encouraging customers to continue conducting business with the city remotely and electronically, as physical distancing standards are practiced at city facilities and many employees continue to work from home,” the statement said.

Elsewhere in the United States:

  • Officials in Arizona on Tuesday announced more than 3,500 new cases and a single-day record for the number of deaths, more than 90. More than 50 of those deaths were in Maricopa County, which includes Phoenix. Twenty were reported in Pima County, which includes Tucson. Relatively few deaths were reported in Arizona over the holiday weekend, which may have contributed to Tuesday’s spike.

  • Officials in Montana announced more than 70 new cases on Tuesday, a single-day record in that state. More than 50 of those cases were in Yellowstone County, which includes Billings.

  • Gov. Tate Reeves of Mississippi, a Republican, said his virus test came back negative after he was screened following his exposure to a member of the state’s legislature last week who tested positive.

  • Nearly 350 public health organizations and agencies released a letter Tuesday to Alex M. Azar II, the health and human services secretary, urging him to champion the Centers for Disease Control and Prevention and other public health agencies amid “increasing reports of resistance” to their recommendations for fighting the virus.

  • The governor of Ohio issued an order requiring residents to wear masks in public in seven counties that are seeing serious growth in cases, including the counties that contain Columbus, Cincinnati and Cleveland. “This is aimed specifically at the seven counties where we are the most concerned,” Gov. Mike DeWine, a Republican, said at a news conference.

Prime Minister Justin Trudeau at the House of Commons in Ottawa in June.Credit...Sean Kilpatrick/The Canadian Press, via Associated Press

Since the pandemic began, Canadians have parsed Prime Minister Justin Trudeau’s every move, from his beard and hair length to his juggling of child-care duties while running the country.

So it did not go unnoticed when Mr. Trudeau announced on Monday that he would not be attending a meeting in Washington this week with Mr. Trump and President Andrés Manuel López Obrador of Mexico to celebrate the start of a seminal new trade deal between the three countries.

That Mr. Trudeau would choose not to fly to Washington to celebrate what many consider one of his most important accomplishments to date was striking. He cited scheduling conflicts as his reason for not attending the meeting, set to begin on Wednesday.

But political analysts saw something else at work: the prime minister has become the country’s model for following medical guidelines on virus prevention — including wearing a mask and avoiding travel — which have become contentious in other countries.

“I don’t think Trudeau has any interest in being drawn into American debates on mask-wearing and appropriate health precautions during an epidemic,” said Roland Paris, a professor of international affairs at the University of Ottawa, and a former foreign policy adviser to Mr. Trudeau.

It would also look hypocritical for the prime minister to dash into the United States for a quick trip when his government officially shut the border in March to anything but essential travel, experts said. (Polls have consistently shown the majority of Canadians want the U.S.-Canada border to remain closed for safety reasons.)

While Mr. Trump has continually underplayed the severity of the virus, and even mocked people for wearing masks, Mr. Trudeau became the first G7 leader to self-isolate after his wife came down with flulike symptoms and later tested positive for Covid-19 in March.

Not everyone agreed about the wisdom of Mr. Trudeau staying away. Mr. Trump “may take this as a slight,” said John Higginbotham, a senior fellow at Carleton University in Ottawa.

With the virus raging in many parts of the United States, new restrictions have left many wondering about the safety of a backyard barbecue or picnic. Here are some tips to help.

Reporting was contributed by Geneva Abdul, Manuela Andreoni, Dan Bilefsky, Julia Calderone, Letícia Casado, Niraj Chokshi, Michael Cooper, Caitlin Dickerson, Manny Fernandez, Michael Gold, Abby Goodnough, Jenny Gross, Maggie Haberman, Mike Ives, Niki Kitsantonis, Isabella Kwai, Ernesto Londoño, Apoorva Mandavilli, Jeff Mays, Giulia McDonnell Nieto del Rio, Patrick McGeehan, Sarah Mervosh, Claire Moses, Elian Peltier, Catherine Porter, Dagny Salas, Michael D. Shear, Mitch Smith, Katie Thomas, David Waldstein, Michael Wines, Sameer Yasir and Karen Zraick.