The choice of Dr. Jha, an outspoken public health expert, is a sign that the White House believes the country is entering a new phase of the pandemic.WASHINGTON — Jeffrey D. Zients, an entrepreneur and management consultant who steered President Biden’s coronavirus response through successive pandemic waves and the largest vaccination campaign in American history, plans to leave the White House in April to return to private life, President Biden said in a statement.Mr. Biden called Mr. Zients “a man of service” and praised his work to “build the infrastructure we needed to deliver vaccines, tests, treatment and masks to hundreds of millions of Americans.”Mr. Zients will be replaced as the White House Covid coordinator by Dr. Ashish K. Jha, the dean of the Brown University School of Public Health and a practicing internist who has urged an aggressive approach to the pandemic in frequent television appearances.Dr. Jha, who is also a health policy researcher with expertise in pandemic preparedness and response, will coordinate the government’s Covid response from inside the White House, officials said.But the selection of a veteran public health expert signaled that Mr. Biden believes the country has moved into a new phase of the fight against the virus.With much of the country vaccinated, officials said the federal response would become more of a long-term public health effort and less of a moment-by-moment crisis requiring rapid government action. If new variants of the virus spread, they said, Dr. Jha will be able to draw upon the tools his predecessor put in place during the past 14 months.In his statement, Mr. Biden said that “Americans are safely moving back to more normal routines, using the effective new tools we have to enable us to reduce severe Covid cases and make workplaces and schools safer.”But he added that “our work in combating Covid is far from done” and called Dr. Jha the “perfect person” to fight the virus “as we enter a new moment in the pandemic.”Officials said his background as a medical doctor makes him the right choice as the virus becomes more an endemic part of the country’s health challenges. In 2014, Dr. Jha was a co-chair of an international commission on the global response to the Ebola outbreak. And he has argued that agencies like the World Health Organization are critical in dealing with diseases like Ebola and Zika.Mr. Zients, 55, became one of the unlikely faces of the Biden administration’s response to the deadly virus, a somber-sounding businessman presiding over weekly updates with public health officials that were streamed live on the White House website. He had committed to working in the West Wing for a limited time as Mr. Biden’s coronavirus response coordinator, and extended his stay several times at the president’s request, officials said.Mr. Zients’s deputy, Natalie Quillian, will also depart in April.Ron Klain, the White House chief of staff, called Mr. Zients a “once-in-a-generation managerial talent” and a “warmhearted friend.” He praised Mr. Zients for his work on getting Americans access to vaccines and tests.“Today, over 215 million Americans are fully vaccinated, Americans have received over one billion at-home tests, 98 percent of schools are open and our economy is recovering,” Mr. Klain said in a statement. “Through the ups and downs of this past year, Jeff met every challenge with a level head and laser-focused execution. Because of that, lives have been saved here at home and in countless other countries.”Mr. Zients’s decision comes as the United States is easing out of pandemic crisis mode for now, but is still not out of danger. While cases are on a downward trajectory in much of the country, they are rising in parts of Europe and Asia. Dr. Anthony S. Fauci, the president’s top medical adviser for the pandemic, said in an interview on Wednesday that they are likely to eventually rise here as well.Addressing them will now be Dr. Jha’s responsibility.Jeffrey Zients’s decision comes as the United States is easing out of pandemic crisis mode for now, but is still not out of danger.Pete Marovich for The New York TimesAt the weekly briefings, Mr. Zients was joined by Dr. Fauci; Dr. Rochelle P. Walensky, the director of the Centers for Disease Control and Prevention; and sometimes Dr. Vivek H. Murthy, the surgeon general.But behind the scenes, he is a logistics man who manages a vast operation that has cost taxpayers trillions of dollars. He has spent much of his time in sometimes intense meetings with drug and insurance company executives, governors, and state and local health officials.Recently, he helped orchestrate the delivery of nearly 400 million N95 masks to Americans, free of charge. And officials said his discussions with Pfizer, the pharmaceutical giant, helped shave months off the development of the company’s antiviral pill; the government has committed to buying 20 million doses.When transportation became a barrier to vaccination, Mr. Zients persuaded the chief executives of Uber and Lyft to offer free rides, said Dr. Marcella Nunez-Smith, who advised the White House on racial equity issues. When lack of child care and vacation leave became obstacles, he persuaded day care centers to offer free care and companies to offer free time off.“I could call him any time of the day or night and say, ‘This is a problem, we’ve got to solve for this,’” she said. “Jeff’s job all day was solving for this.”Critics have said Mr. Zients, who made a fortune building two consultancies and taking them public, was an odd pick to run the pandemic response given his lack of experience in public health. But his past work touched on health care, both as the chief executive of the Advisory Board Company, a health care consultancy, and in the Obama administration, where he ran the effort to fix the healthcare.gov website.During the surge of cases — and deaths — this winter, some blamed Mr. Zients for failing to do enough to prevent them, particularly when the highly transmissible Omicron variant caught the administration unprepared. Some supporters of Mr. Biden — particularly those on the Democratic left — were openly disdainful of both Mr. Zients and Mr. Klain.“We wanted this to be run as a scientific operation; it’s being run as a management consultancy,” Gregg Gonsalves, a longtime AIDS activist and epidemiologist at Yale University, said in an interview in January. “Ron Klain and Jeff Zients are the wrong people to be where the buck stops on this.”In January, The American Prospect, a liberal website, published an article titled “Fire Jeff Zients” that said he had “proven himself not up to the task, and Biden should relieve him of his duties.”Mr. Zients was not always able to see around corners. In June, he declared that the nation was “entering a summer of joy, a summer of freedom,” not long after the Delta variant hammered India, and as it hit Britain. When it took hold in the United States over the summer, cases and deaths skyrocketed.Critics pointed to the White House’s failure to ensure enough supply to meet the huge demand for mass rapid testing in the weeks before and after Christmas, a logistics problem that lingered well into January, as the Omicron surge began receding.Dr. Fauci, though, defended Mr. Zients, saying his predictions last summer were based on the assumptions — incorrect, as it turned out — that 70 percent of the adult population would be vaccinated by July 4, and that the coronavirus could not spread among vaccinated people.Dr. Fauci said Mr. Zients was always calm in a crisis, likening him to a hockey player who “always looked at where the puck is going to be, as opposed to where the puck is.” At the moment, Mr. Zients is trying to persuade Congress to appropriate $22.5 billion in coronavirus relief funds that the administration says it desperately needs to purchase more tests, drugs and vaccines.In an interview on Tuesday, he expressed confidence that lawmakers would approve the funds without strings attached, despite demands from Republicans for the White House to come up with a plan to pay for the aid package by diverting existing money from other programs.Congress was poised to pass the package last week, but it fell apart after governors, and House Democrats, objected to paying for it in part by taking $7 billion in federal money that had been allocated to the states. The White House said on Tuesday that it had already scaled back plans to buy monoclonal antibody treatments because the government was out of cash.“We’ve got to get it done,” Mr. Zients said. “Because there are major consequences to not getting it done.”The decision to replace Mr. Zients with Dr. Jha reflects Mr. Biden’s desire to keep management of the pandemic close at hand.Previous public health crises have been managed by officials at the Department of Health and Human Services, which oversees the C.D.C. and the Food and Drug Administration. But that has not been the case during the coronavirus pandemic, either under Mr. Biden or his predecessor, President Donald J. Trump.Both presidents chose to anchor their response to the virus in the West Wing. Biden administration officials say that because the fight against Covid-19 requires a “whole of government” response, involving multiple agencies, it makes sense to keep it centered in the White House.A native of India who immigrated first to Canada and then to the United States, Dr. Jha is a general internist who has practiced in Massachusetts and Providence, R.I. Before taking the position at Brown in the fall of 2020, he directed a global health institute at Harvard University’s School of Public Health.He has been a strong advocate for expanding global access to Covid-19 vaccines, and pushed the nascent Biden administration to take an aggressive stance in a February 2021 article in Foreign Affairs.“What that led to is a call with a couple of people on the Biden team who asked, ‘Do you think we’re not being aggressive enough?’” he said in an interview at the time. He told them that while the administration’s efforts looked “heroic” compared with those of Mr. Trump, they were indeed inadequate for the crisis at hand.

Contracts to purchase tests could be signed as soon as next week, but relief could be weeks away for people trying to buy the hard-to-find tests.WASHINGTON — President Biden promised Americans he is making 500 million coronavirus tests available free of charge, but help is at least weeks away — if not longer — for anxious Americans facing a surge of new virus cases.Mr. Biden’s administration has not yet signed a contract to buy the tests, and the website to order them will not be up until January. Officials have not said how many tests people will be able to order or how quickly they will be shipped once they begin to be available next month. Manufacturers say they are already producing tests as fast as they can.As a candidate, Mr. Biden excoriated the lack of testing during the Trump administration, saying in March 2020 that “the administration’s failure on testing is colossal, and it’s a failure of planning, leadership and execution.” But the Omicron variant caught the White House off guard, as the president has acknowledged, and cases have far outstripped the government’s ability to make tests available.The president’s pledge of a half-billion tests on Tuesday was the centerpiece of a newly aggressive testing effort, announced just days before Christmas, as Americans try to find the hard-to-find tests so they know whether they are infected during the holiday season.“That’s not a plan — it’s a hope,” said Jennifer Nuzzo, an epidemiologist at the Johns Hopkins Bloomberg School of Public Health, which tracks testing trends. “If those tests came in January and February, that could have an impact, but if they are spread out over 10 to 12 months, I’m not sure what kind of impact it is going to have.”Contracts to purchase tests could be finalized as soon as next week, officials said.Whether testing manufacturers can now ramp up to produce an extra 500 million at-home tests — and how soon — is unclear. John M. Koval, a spokesman for Abbott Laboratories, a major manufacturer of rapid at-home antigen tests, said in an email message that the company is seeing “unprecedented demand” for its tests, “and we’re sending them out as fast as we can make them.”The company is running its manufacturing plants around the clock, investing in automation and hiring more workers, Mr. Koval said. Abbott will make 70 million tests in January, he said, and “can scale significantly in the months ahead.”Ellume, an Australian manufacturer of a competing rapid test, said in a statement that it “stands ready to meet the increased demand” by supplying the government 8.5 million tests, and opening a new manufacturing facility in Frederick, Md., in January. Once fully operational, that plant will produce 15 million tests a month.The shortage of tests comes as Americans want to know whether they are infected during the holiday season.Saul Martinez for The New York TimesThe Biden plan is facing competition from state and local officials who got out ahead of the president. In Maryland, Gov. Larry Hogan announced last month that his administration was making 500,000 Abbott at-home tests available. Colorado began distributing free at-home tests in October. Dozens of cities and towns in Massachusetts are already sending out free tests under a new statewide program.Experts say it is unlikely that the 500 million new tests will become available all at once. Dr. Michael Mina, an epidemiologist and former Harvard professor who has repeatedly called for expanded use of testing, said he expected that they would be distributed over two to three months.“Had this been started a long time ago, maybe things would be a bit different,” said Dr. Mina, who recently became the chief science officer of eMed, which distributes at-home tests. “But this is where we are now, and we kind of have to deal with it.”Shortages of at-home tests are not unique to the United States. In the last week, headlines have blared about long lines for testing in Spain, Britain, Canada, Germany and Ireland.The White House also noted that the government has increased other methods of testing over the past several months, including sending 50 million free tests to community health centers and help to hot spots.By next week, a team from the Centers for Disease Control and Prevention will be in New York City helping to provide an additional 25,000 of the more sensitive laboratory-conducted tests. The first mobile site opened in Queens on Wednesday, and two more will open Thursday in Flushing and East Elmhurst, New York officials said.Jen Psaki, the White House press secretary, said Wednesday that the 500 million tests are “the biggest purchase that we have done to date.”“It certainly represents a significant commitment, a recognition by the president that we need to be doing more,” she said.For Mr. Biden, the scramble to address the shortfall in the availability of testing is an uncomfortable parallel with the Trump administration’s inability to roll out testing at the beginning of the pandemic in 2020.Mr. Biden acknowledged that the Omicron surge caught the White House off guard.Stefani Reynolds for The New York TimesThe Trump administration struggled with supply shortages and a president who complained that testing was driving up caseload reports and making him look bad.Mr. Biden came into office vowing to expand the supply of tests but later focused his response almost exclusively on vaccines, and demand for testing fell so low that Abbott destroyed millions of tests in August — just as the Delta variant was surging.The Coronavirus Pandemic: Key Things to KnowCard 1 of 4The Omicron variant.