The news Monday that Pfizer’s coronavirus vaccine is more than 90 percent effective sharply increased prospects that federal regulators will authorize the vaccine on an emergency basis as early as mid-December, and that the first shots will be administered before the end of the year or early next year.

The findings, announced by drug giant Pfizer and German biotechnology firm BioNTech, provided much-needed hope for a nation battered by surging virus cases, a stumbling economy and a bitterly fought presidential campaign. It augers well for other vaccines and could accelerate the timetable for reining in the pandemic, said scientists, who cautioned that any successful vaccine will still face obstacles, notably distribution to hundreds of millions of people.

“It’s stunning,” said Eric Topol, director of the Scripps Research Translational Institute, one of several scientists who said they were heartened by the results, which far exceeded the Food and Drug Administration’s standard that a vaccine be more than 50 percent effective at protecting people compared with a placebo saline shot. “We could have a rollout in December.”

Even with the welcome development, experts warned that the longed-for return to normalcy will take many months or more, and that the path is certain to contain unexpected twists and turns. Even after a vaccine is approved, they said, people will need to wear masks and social distance for some time – in part because the vaccine doses will be limited, and it will take time to immunize enough of the population to stop the virus from spreading.

As if to underscore the difficult days ahead, the United States on Monday hit the latest grim milestone in the pandemic, surpassing 10 million confirmed cases of COVID-19, the disease caused by the coronavirus, along with more than 238,000 deaths.

The unchecked spread of the virus threaten to make the coming weeks and months particularly dangerous for the nation, which still has little semblance of a coherent federal strategy to stem the tide of infections. And as yet another member of the Trump administration – Housing and Urban Development Secretary Ben Carson – tested positive for the virus, President-elect Joe Biden on Monday named his coronavirus task force, made up of scientists and physicians, vowing in a speech to “follow the science” when he takes office in January. But he warned that the nation still faces “a very dark winter.”

Still, the vaccine news buoyed scientists who have spent months battling a seemingly implacable foe.

“We will be giving vaccines to people very likely before the end of this year,” Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, predicted on CNN.

Scott Gottlieb, a former FDA commissioner in the Trump administration and member of Pfizer’s board, said if a vaccine were authorized by mid-to-late December, it would be available for the general public late in the second quarter or early in the third quarter of next year. In addition to Pfizer, Moderna, a biotech firm using a technology similar to Pfizer’s, might apply to the FDA for authorization in the next several weeks, company officials have said.

Fauci said in a separate interview with The Washington Post that although it was too soon to predict when the world would return to normal, “The more effective a vaccine is, the quicker you get to the point where you can get a degree of immunity in the general population, to allow you to get back to some sort of normalcy.” He predicted that a highly effective vaccine means “there will be more enthusiasm” among the public about receiving it.

Still, experts said, more information is needed on the Pfizer vaccine, including how long its protection lasts, how well it protects people in specific groups such as the elderly, and whether it causes side effects. Company officials said Monday it didn’t seem to cause serious safety problems.

In announcing the vaccine data, Pfizer and BioNTech said they plan to submit an application for emergency authorization to the FDA probably the third week of November, after receiving additional information on safety and the manufacturing process. The trial will continue until it reaches its endpoint of 164 cases of the coronavirus, which Jansen said could take a few weeks. The additional data could influence the effectiveness of the vaccine.

The agency has said it will convene its outside advisory committee to consider each vaccine application; a meeting on the Pfizer vaccine could occur in early December, with the agency making a final decision days or weeks afterward.

If the vaccine is cleared by the FDA, an advisory panel to the Centers for Disease Control and Prevention – the Advisory Committee on Immunization Practices – is expected to hold a public meeting within 24 to 48 hours to vote on how the vaccine should be used and who should get the first shots. Its recommendations will go to the CDC director for approval. After that, federal officials have said, they plan to start shipping vaccine vials as soon as possible – probably within a day or two.

Pfizer has projected having 50 million doses – enough for 25 million people – by the end of the year, and 1.3 billion doses in 2021. On CNBC, Pfizer chief executive Albert Bourla said the company was examining ways to increase production.

“We are aware that the demand will be much higher than anything we can produce. We are also looking right now to see if there are other ways, thinking out of the box, that we can increase even further the manufacturing capacity,” Bourla said.

In talking about multiple vaccine candidates, officials with Operation Warp Speed, the government initiative designed to expedite development of vaccines and therapeutics, have repeatedly projected having 100 million doses available by the end of the year, and 600 million to 700 million doses by March or April. That does not ensure that all those vaccine candidates will be proven safe and effective. Along with Pfizer and Moderna, several other companies are working on coronavirus vaccines.

The challenges in distributing the Pfizer vaccine, which must be stored at ultracold temperatures of -74 Fahrenheit can’t be overstated.

“It’s a nontrivial thing to distribute tens of millions of doses, and it has to be given twice,” said John Moore, a virologist at Weill Cornell Medicine. “We won’t be going to motor-biker rallies in the foreseeable future.”

The CDC, which is coordinating the distribution with the Defense Department, has asked states to provide a list of each jurisdiction’s top five sites capable of receiving and administering a vaccine with these ultracold requirements. The ultracold requirement and minimum orders of about 1,000 doses mean that most doctors’ offices will not have the ability to stock it. Hospitals and other institutions that have the necessary freezer storage are likely to be the first to administer the shots.

“It needs to be a perfectly choreographed dance, and we haven’t even started rehearsals yet,” said Soumi Saha, vice president of advocacy at Premier, a major group purchasing organization for hospitals.

Limited initial doses are likely to go first to health care workers, members of the advisory committee on immunization have said. Three additional groups are likely to be close behind: essential workers, people 65 and older, and individuals with underlying medical conditions that put them at higher risk of getting very sick with COVID-19.

Close to 200 million people total are in those groups, according to immunization committee estimates.

The federal government will make recommendations on who should have priority to get the vaccine, and make allocations to the states. The final decision rests with states, which have been planning in earnest in recent weeks to get shots into arms.

Local officials still need to recruit thousands of people to staff vaccine clinics and enroll and train providers. They also have to ramp up information technology and data systems to track vaccine inventory and ordering to ensure people get the correct doses at the right times – most vaccines will require two shots – and to monitor for adverse events.

Beth Bell, a member of the immunization committee who also chairs the panel’s COVID-19 vaccines work group, said she was hopeful Americans would start having more-normal lives next summer or fall. That assumes, she said, the nation has several effective vaccines by then and that the “virus doesn’t throw us any curveballs and, very importantly, that people have confidence in the vaccination program and are willing to be vaccinated.”

If there are setbacks, “People need to be a little bit calm and to expect bumps in the road and not overreact to them,” said Bell, a global health professor at the University of Washington and former top CDC official overseeing infectious diseases. “I know we’re all sick of the pandemic … but we need to keep at it, go forward deliberatively and calmly.”

Peter Lurie, a top FDA official during the Obama administration, agreed much more information is needed about the Pfizer vaccine and that challenges in distributing it lie ahead. “But today is a brighter day,” he said. “And as the scientific and regulatory processes unfold, we will soon know how bright.”

The immunization committee has been holding special meetings to review data on the virus and the vaccines in development, including one last month. Members will review demographic data about the people receiving the vaccine, how different groups responded and side effects before making recommendations.

William Schaffner, an infectious-disease expert at the Vanderbilt University School of Medicine, said he hoped Thanksgiving 2021 would be far different from this year’s holiday.

“We will get back to something that is near normal, but it won’t be exactly the old normal,” he said. “This and the other vaccines won’t be a magic wand – they will be additional barriers to the transmission of the virus.”

Still, he and others said, the virus will become like the flu – it won’t go away, but humans will have learned to live with it.

Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia, noted that tens of thousands of people die of the flu every year, but it doesn’t end Americans’ activities.

“We live with that, I go to Eagles games,” he said. “I feel comfortable I’m not going to be one of those people who die of the flu. The question is – when will we feel that way about the coronavirus?”