Two days after U.S. deaths surpassed 150,000, three familiar federal health officials, including Dr. Anthony S. Fauci, returned to Capitol Hill to testify in front of a new audience: the House’s special select committee investigating the Trump administration’s response to the pandemic.

Dr. Fauci, the nation’s top infectious disease expert, was joined on Friday morning by Dr. Robert R. Redfield, the director of the Centers for Disease Control and Prevention, and Adm. Brett P. Giroir, the assistant secretary for health and the administration’s point person on coronavirus testing.

Representative Jim Clyburn of South Carolina, the top Democrat on the House committee charged with overseeing the response to the coronavirus, kicked off the hearing by demanding that the Trump administration put forth a “comprehensive national plan” to control the pandemic.

“It is clear that the administration’s approach of deferring to the states, sidelining the experts and rushing to reopen has prolonged this virus and led to thousands of preventable deaths,” said Representative Jim Clyburn of South Carolina, the Democratic chairman of the House select committee overseeing the coronavirus responses.

The top Republican on the panel, Representative Steve Scalise of Louisiana, chided Mr. Clyburn for advancing a political narrative. Turning to the witnesses, he said: “You wouldn’t even be here today if there wasn’t a plan”

The three witnesses last testified a month ago before lawmakers in the Republican-controlled Senate, when the subject was school reopening.

But the Democrat-led House select committee has had a hard time securing Dr. Fauci and his colleagues as witnesses. The Trump administration initially refused to make them available.

The hearing is taking place as states across the country are reimposing limits in response to a resurgence of cases — a turn of events reflected in the title lawmakers gave the hearing: “The Urgent Need for a National Plan to Contain the Coronavirus.”

With President Trump clearly intent on announcing promising vaccine news, it has fallen to Dr. Fauci to offer reassurances that the federal government is moving quickly but safely.

Dr. Fauci reassured Congress that the United States would likely have a vaccine by the end of this year or early in 2021, and said Americans would not have to depend on other countries for coronavirus immunization.

He cast doubt on some foreign efforts, saying, “I do hope that the Chinese and the Russians are actually testing the vaccine before they’re administering the vaccine to anyone.”

The virus panel was established this spring by Speaker Nancy Pelosi in large part to put a check on how the federal government is spending the trillions of dollars in emergency aid. But its mandate has broadened to include a panoply of issues, including racial disparities in the pandemic and nursing home outbreaks.

Earlier this month, the Trump administration ordered hospitals to bypass the Centers for Disease Control and Prevention and send all Covid-19 patient information to a central database in Washington, a move that alarmed health experts who feared the data will be politicized or withheld from the public.

Dr. Redfield testified that “we weren’t directly involved in the final decision” to strip his agency of authority to collect the data, and said, “I was told actually when the secretary’s office made the decision.”

Some of the House’s fieriest members are on the panel, including Representative Jim Jordan, an Ohio Republican who has been a regular skeptic of Dr. Fauci and public health mandates, including mask wearing.

Dr. Fauci and Mr. Jordan had a testy exchange when Mr. Jordan pushed Dr. Fauci to say that protests should be limited or shut down over virus concerns in crowds. “I’m not going to opine on limiting anything,” Dr. Fauci said, adding, “I don’t judge one crowd versus another crowd.”

Several of the panel’s prominent Democrats are also not known for shying away from conflict, including Mr. Clyburn and Representative Maxine Waters of California.

The French drug maker Sanofi said on Friday that it had secured an agreement of up to $2.1 billion to supply the United States government with 100 million doses of its experimental coronavirus vaccine, the largest such deal announced to date.

The arrangement brings the Trump administration’s investment in coronavirus vaccine projects to more than $8 billion. This sprawling, multiagency effort, known as Operation Warp Speed, is placing bets on multiple vaccines and is paying companies to manufacture millions of doses before clinical trials have been completed.

“The global need for a vaccine to help prevent Covid-19 is massive, and no single vaccine or company will be able to meet the global demand alone,” Thomas Triomphe, executive vice president and global head of Sanofi Pasteur, the company’s vaccine division, said in a statement.

Under the deal announced, Sanofi and its partner, the British pharmaceutical company GlaxoSmithKline, will receive federal funding to pay for clinical trials as well as for manufacturing the vaccine. Sanofi said the deal also includes an option for the company to supply an additional 500 million doses. The company expects to begin clinical trials to test for safety in September, followed by late-stage efficacy trials before the end of this year. Sanofi said it could apply for regulatory approval in the first half of next year.

If the vaccine is successful, it would be made available to Americans at no cost, other than what providers charge to administer it, the federal government said in a statement.

The head of Operation Warp Speed, Moncef Slaoui, is a former GSK executive who as of May held just under $10 million in GSK stock. Dr. Slaoui’s financial ties to some of the companies that are pursuing coronavirus vaccines have raised questions about conflicts of interest.

Sanofi and GSK did not say how much of the federal money would go to each company — only that Sanofi would receive the most. GSK did not comment on whether Dr. Slaoui had recused himself from negotiations over the deal. A senior administration official said all agreements were negotiated by federal “acquisition professionals” and that Dr. Slaoui did not play a role in the negotiations.

When the coronavirus erupted in the West, Italy was the nightmarish epicenter, a place to avoid at all costs and a shorthand in the United States and much of Europe for uncontrolled contagion.

Fast forward a few months, and the United States has suffered tens of thousands more deaths than any country in the world. European states that once looked smugly at Italy are facing new flare-ups.

And Italy? Its hospitals are basically empty of Covid-19 patients. Daily deaths attributed to the virus in Lombardy, the region that bore the brunt of the pandemic, hover around zero. The number of new daily cases has plummeted to “one of the lowest in Europe and the world,” said Giovanni Rezza, director of the infective illness department at the National Institute of Health.

How Italy has gone from being a global pariah to a model — however imperfect — of viral containment holds fresh lessons for the rest of the world, including the United States.

Italy has consolidated, or at least maintained, the rewards of a tough nationwide lockdown through a mix of vigilance and painfully gained medical expertise.

• Its government has been guided by scientific and technical committees.

• The country set aside economic pressures and only began easing its exceptionally tight lockdown based on case counts.

• Italy continues to limit travel from elsewhere.

• Local doctors, hospitals and health officials collect more than 20 indicators on the virus daily and send them to regional authorities, who then forward them to the National Institute of Health.

The result is a weekly X-ray of the country’s health upon which policy decisions are based. That is a long way from the state of panic, and near collapse, that hit Italy in March.

The European economy tumbled into its worst recession on record in the second quarter, as quarantines across the continent brought business, trade and consumer spending to a grinding halt.

From April to June, gross domestic product fell by 11.9 percent from the first quarter in the 27 member states of the European Union, and by 12.1 percent in the core group of countries that use the euro currency, according to figures released on Friday by Eurostat, the E.U. statistics agency.

On an annualized basis, European Union economies shrank by 14.4 percent, and eurozone economies by 15 percent, the sharpest contractions since statistics started being kept in 1995.

Over the same period, the United States economy shrank by 9.5 percent on the previous quarter and by 32.9 percent on an annual basis, according to figures published on Thursday.

But in Europe, there were signs that the worst may have passed, and that a tentative recovery has been gaining some traction as governments unleash enormous stimulus spending. Lengthy lockdowns, while painful for business and industry, have helped curb a widespread resurgence of the pandemic in most countries, easing reopening.

The figures were especially grim for nations on Europe’s southern rim, which were among the worst affected by the virus and which faced longer quarantine periods than northern European countries.

In Spain, which has had one of Europe’s highest death tolls, the economy shrank by a staggering 22.1 percent from a year ago and by 18.5 percent from the first quarter. France, the eurozone’s second-largest economy, shrank by 19 percent from a year ago and by 13.8 percent from the first quarter; and Italy, the third-largest economy in the zone, contracted by 17.3 percent from a year ago and by 12.4 percent from the first quarter. France is officially in recession, with three straight quarters of contraction.

On Thursday, the authorities reported that the German economy, Europe’s largest, shrank by 11.7 percent from the same period last year and by 10.1 percent from the previous quarter.

European Union leaders last week agreed to a landmark stimulus of 750 billion euros, or about $884 billion, to rescue their economies and to anchor a mild turnaround that had started to take hold after lockdowns began to be lifted.

But risks abound as surges in new cases are reported, increasing the possibility of more quarantines.

“The hard part of this recovery is set to start about now,” Bert Colijn, senior economist for the eurozone at ING Bank, said in a note to clients.

New York City public schools, the nation’s largest school system, will be able to reopen its school buildings in September only if the city maintains a test positivity rate below 3 percent, Mayor Bill de Blasio announced on Friday. That conservative threshold is even lower than the 5 percent test positivity rate which has been set by Gov. Andrew M. Cuomo as a cut-off for school reopening and recommended by public health experts.

The average positivity for New York City has generally remained lower even than the new city threshold, according to city and state figures. But even a modest uptick in cases over the next few weeks could nudge that rate closer to the new threshold, which raises fresh questions about whether city schools will open part-time on Sept. 10 as planned in a hybrid model.

“I want to set that very very tough standard,” the mayor said, adding, “this is a way of proving that we will do things the right way.”

New York is one of the only large districts in the country that is currently planning to reopen its buildings at all: Children will report to school one to three days a week to allow for social distancing. All staff members will be asked to take tests before the start of school, with expedited results. Education officials in the city laid out a plan on Thursday for what would happen in the seemingly inevitable event that cases are confirmed in a classroom.

The protocol means it is likely that at many of the city’s 1,800 schools, individual classrooms or even entire buildings will be closed at points during the school year.

Officials said confirmed infections among students, teachers and staff members would be treated the same. One or two cases in a single classroom would require those classes to close for 14 days; all students and staff members in that classroom would be ordered to self-quarantine, and students would learn remotely. The rest of the school would continue to operate.

But if two or more people in different classrooms in the same school tested positive, the entire building would close while disease detectives from the city’s Department of Health were brought in to investigate the cases, which could take several days. Depending on the results of the investigation, the building could reopen, but the classrooms with positive cases would remain closed for 14 days.

If disease detectives were not able to find a link between two or more confirmed cases in a building, including exposure to the virus outside of school, the entire building would remain shuttered for two weeks.

Mr. de Blasio’s administration faced enormous criticism for waiting until mid-March to close schools, after the virus had already begun to spread significantly throughout the city, which soon became a global center of the crisis. Throughout March, when a student or staff member tested positive, the school would automatically close for 24 hours for cleaning, a protocol that many parents and teachers said was too lax.

Other states, including California, have announced less stringent policies for how to manage positive cases in schools. But most California school districts will begin the academic year exclusively online because of the high numbers of cases in their communities.

Native Americans appear to be hit particularly hard by the virus, though the data is incomplete.

Even with significant gaps in the available data, there are strong indications that Native American people have been disproportionately affected by the virus.

The rate of known cases in the eight counties with the largest populations of Native Americans is nearly double the national average, a New York Times analysis has found. The analysis cannot determine which individuals are testing positive for the virus, but these counties are home to one in six U.S. residents who describe themselves in census surveys as non-Hispanic and American Indian or Alaska Native.

And there are many other smaller counties with significant populations of Native Americans that have elevated case rates, including Yakima County, Wash. The Times identified at least 15 counties that have elevated case rates and are home to sizable numbers of Native American residents, ranging from large metropolitan areas in Arizona to rural communities in Nebraska and Mississippi.

“I feel as though tribal nations have an effective death sentence when the scale of this pandemic, if it continues to grow, exceeds the public resources available,” said Fawn Sharp, the president of the Quinault Indian Nation and of the National Congress of American Indians.

The trends are troubling enough that congressional leaders have asked the U.S. Commission on Civil Rights to examine them.

In New Mexico, Native American and Alaska Native people have accounted for nearly 40 percent of virus cases, though they make up 9 percent of the population.

Hospitalization rates published by the Centers for Disease Control and Prevention also suggest that Native American people are overrepresented among those who become seriously ill from the virus. Federal data tracking individual coronavirus cases often omits race and ethnicity information.

Native Americans — particularly those living on reservations — are more prone to contract the virus because of crowded housing conditions that make social distancing difficult, said Allison Barlow, director of the Center for American Indian Health at Johns Hopkins University. And years of underfunded health systems, food and water insecurity and other factors contribute to underlying health conditions that can make the illness more severe once contracted.

The Hong Kong government said on Friday that it would postpone the city’s September legislative election by a year because of the coronavirus pandemic, a decision seen by the pro-democracy opposition as a brazen attempt to thwart its electoral momentum and avoid the defeat of pro-Beijing candidates.

“It is a really tough decision to delay but we want to ensure fairness, public safety and public health,” said Carrie Lam, Hong Kong’s chief executive.

The delay was a blow to opposition politicians, who had expected to ride to victory in the fall on a wave of deep-seated dissatisfaction with the government and concerns about a sweeping new national security law imposed on the city by Beijing. And it was the latest in a quick series of aggressive moves by the pro-Beijing establishment to sideline the pro-democracy movement.

On Thursday, 12 pro-democracy candidates said they had been barred from running, including four sitting lawmakers and several prominent activists like Joshua Wong. Mr. Wong said he was barred in part because of his criticism of the new security law. He called the disqualifications “the most scandalous election fraud ever in Hong Kong history.”

Even as Hong Kong cast the decision as one made for public health reasons, to curb the spread of the virus, the pro-democracy opposition has accused the government of using social-distancing rules to clamp down on the protest movement that began more than a year ago.

Britain has barred millions of people in northern England from meeting other households at their homes, paused reopenings set for Aug. 1 and moved to make face masks mandatory in more places, after a day on which it reported 38 new coronavirus deaths and nearly 900 known new infections, its highest case numbers in a month.

At a news conference on Friday, Prime Minister Boris Johnson said he had promised to put on the brakes at any sign of an increase in cases, and added: “Our assessment is that we should now squeeze that brake pedal.”

Britain — which has suffered Europe’s worst coronavirus outbreak, with nearly 56,000 confirmed deaths — has been gradually easing restrictions, with pubs, restaurants, museums and hair salons allowed to reopen early this month.

On Saturday, the government had planned to allow reopening of higher-risk settings in England including casinos, bowling alleys and skating rinks, and to permit small wedding receptions and some indoor performances. All that will now be pushed back until at least August 15.

“We simply cannot take the risk,” Mr. Johnson said. “We will of course study the data carefully and pay attention to open up as soon as we can.”

Measures to encourage more people to return to their places of work would go ahead, he said. Mr. Johnson also added that mask wearing, already mandatory in shops and supermarkets in England, would be extended to include more indoor settings where social distancing was not an option.

The moves came suddenly, with the restrictions in northern England implemented at midnight, less than three hours after the authorities’ initial announcement Thursday night, and with official guidance on what the rules cover not published until the following morning.

Those restrictions affect Manchester and its surrounding towns and suburbs, plus areas in East Lancashire and West Yorkshire.The announcement came just before Eid al-Adha, and several of the affected areas have large Muslim communities. Places of worship will remain open with social distancing measures but the authorities recommended praying outdoors.

Here are other developments from around the globe:

• Vietnam, which has been fighting a fresh virus outbreak after more than three months without reporting a locally transmitted case, has announced its first death from the coronavirus. The victim was a 70-year-old resident of the city of Hoi An who had been living with kidney disease for more than a decade. The man was admitted to a hospital on July 9 with chest tightness and fatigue, and tested positive for the virus on Sunday. He died Friday morning.

• On Friday, Japan announced 1,305 new cases, breaking a record set the day before. As cases spike in Tokyo, Gov. Yuriko Koike has requested that karaoke venues and bars and restaurants serving alcohol close by 10 p.m. from Aug. 3 through the end of the month. Businesses that cooperate will be offered 200,000 yen, or about $1,900.

Many African countries are testing too little to track the virus, an aid group warns.

A stark lack of testing in many African countries has kept officials from being able to track the pandemic, prompting fears that a recent surge in cases across the continent may be just the “tip of the iceberg,” according to the International Rescue Committee.

Each country in Africa where the committee works has conducted fewer than 8,000 tests per million people, the group said. By contrast, Britain has conducted 205,782 tests per million, the United Arab Emirates 472,590 per million, and Singapore 199,904 per million, the committee said.

The committee cited Tanzania (63 tests per million), Niger (373 tests per million), Chad (383 tests per million), Democratic Republic of Congo (467 tests per million) and Burundi (563 tests per million) as having the lowest testing rates among the African countries where it works.

The committee, a global humanitarian aid organization, said that testing in many African countries was falling far short of the rate of at least one test per 1,000 people per week recommended by the World Health Organization.

The organization said many African nations needed international support to increase their testing capacity or the continent could face “an undetected and uncontrolled spread — and a response fighting with a hand tied behind its back.”

“The testing shortfalls make it nearly impossible to understand the extent of the pandemic — let alone put measures in place to stop it,” Stacey Mearns, a senior technical adviser on emergency health at the committee, said in a statement.

Reporting was contributed by Liz Alderman, Julia Calderone, Kate Conger, Robert Gebeloff, Michael Levenson, Giulia McDonnell Nieto del Rio, Eshe Nelson, Richard A. Oppel Jr., Richard C. Paddock, Elian Peltier, Matt Phillips, Austin Ramzy, Motoko Rich, Eliza Shapiro, Megan Specia, Eileen Sullivan, Katie Thomas, Neil Vigdor, Mihir Zaveri.