The federal government could begin distributing two coronavirus vaccines in the next few weeks – a record-shattering accomplishment that now hinges on the decisions of U.S. regulators.

Biotechnology company Moderna filed Monday for emergency authorization of its coronavirus vaccine, capping a scientific sprint that began in January. Moderna’s two-dose regimen is about a week behind a similar vaccine developed by Pfizer and German biotechnology company BioNTech.

No vaccine can arrive soon enough to blunt an anticipated blitz of coronavirus cases seeded by Thanksgiving travels and gatherings – a surge expected to materialize in the coming days and weeks. But less than a year after a novel virus began hopscotching around the world, U.S. government officials project an unprecedented scientific feat: About 40 million doses of two remarkably effective vaccines could be available by year’s end, enough for 20 million people to receive full protection. Manufacturing will continue to ramp up through early next year, and other vaccines are expected to follow to steadily increase the supply available each month.

“You don’t want to get ahead of yourself and claim any victories, but this has the makings of a very, very important positive impact on ending this outbreak,” said Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases. “A vaccine that is highly efficacious, if taken by a very, very high percentage of people, could potentially crush this outbreak – similar to what was done with outbreaks of measles and polio and smallpox and other diseases.”

The news comes as health systems approach a potential crisis with surging daily infections and hospitalizations leading into the Christmas and the new year. The Association of American Medical Colleges on Monday called on the nation’s medical schools, teaching hospitals and health systems to prepare to implement crisis standards over the next few months in case triaging and rationing is necessary as a result of shortages of health-care workers, hospital beds or supplies. Those have been used in response to natural disasters and mass-casualty events such as the Sept. 11 terrorist attacks.

“The next few months of the pandemic, while we are awaiting the distribution of vaccines, are going to stretch the nation’s health-care capacity to its limits,” said the group’s president and CEO, David Skorton.

California Gov. Gavin Newsom, a Democrat, said Monday that he’s considering imposing stay-home orders on California counties to curb an explosion in coronavirus cases that threaten to overwhelm hospitals by Christmas.

Before Thanksgiving weekend, the United States had reached a daily coronavirus death toll not seen since May, as more than 2,000 people died Tuesday through Wednesday. Case counts over weekends and holidays tend to reflect lags in testing and reporting, but hospitalizations continued to climb, surpassing 95,000 covid-19 patients for the first time Monday.

Reflecting the urgency of the situation in the United States, an advisory committee to the Centers for Disease Control and Prevention that typically meets after vaccines are approved is holding an unusual emergency virtual meeting Tuesday to vote on which groups of people should get the first, limited shots. Health-care workers and residents of long-term care facilities are expected to be included in the first case, a strategy intended to ensure that the first doses have the greatest societal impact. But even if manufacturing timelines are on track, there will not be quite enough vaccine for everyone in those groups to be fully vaccinated by year’s end.

“Prioritizing health-care workers first is . . . to keep our health care system functioning and to protect them,” said Natalie Dean, a biostatistician at the University of Florida.

The regulatory approval process will move into high gear Thursday, when independent advisers to the Food and Drug Administration meet to make recommendations about the Pfizer and BioNTech vaccine. A week later, they will do the same for Moderna.

The FDA is undertaking an exhaustive review to vet the safety, effectiveness and manufacturing of the vaccines, and is expected to make a decision shortly after its advisers meet. The review period, from company filing to a decision, probably will take weeks – not the year that is more typical after a company submits a vaccine for approval.

Moderna’s vaccine was 94% effective at preventing illness in a 30,000-person clinical trial, the company said in a news release – a performance that exceeds expectations and is on par with the best pediatric vaccines. There were 196 cases of covid-19, the illness that can be caused by the novel coronavirus, in Moderna’s study, 11 of which occurred in the vaccine group – a decisive signal that the vaccine protected people from illness. The 30 severe cases of covid-19 in the trial, including one death, all occurred in the group that received a placebo.

“The data are very, very promising, but I would like to see more data than is currently in the press release,” said Walter Orenstein, associate director of the Emory Vaccine Center, who is also a member of Moderna’s scientific advisory board and a trial participant. The results are similar to those from Pfizer and BioNTech, which announced a 95% effective vaccine earlier this month.

Even with a vaccine that is very effective, Orenstein cautioned that the world would not snap back to normal. Those first in line to receive two doses of the vaccine probably will be encouraged to continue taking precautions, such as wearing masks, if there is virus circulating at high levels in their communities. Tens of millions more people who are not considered at high risk of severe illness probably will not have access to doses until late spring or summer, experts caution.

The vaccines from Moderna and Pfizer and BioNTech are a major proof of concept for a flexible and fast medical technology, years in the making, that utilizes a snippet of genetic material called messenger RNA that teaches cells to build the spiky protein found on the surface of the coronavirus. The immune system learns to recognize and block the real virus.

The vaccines are on track to make history because of years of basic science research and an all-out coordinated effort from pharmaceutical companies and government that removed the financial risks of failure to move fast.

The U.S. government, through Operation Warp Speed, has preordered 100 million doses from Moderna and Pfizer, and helped underwrite the research and development of Moderna’s vaccine to the tune of $955 million. Moderna also signed a contract to provide 100 million doses to the U.S. for $1.5 billion. Pfizer will provide 100 million doses at a cost of $1.95 billion. In addition, the government has an option to buy hundreds of millions more doses.

“Pfizer and Moderna’s incredibly promising and impressive efficacy data further demonstrate that President Trump’s Operation Warp Speed is rapidly advancing on a trajectory of success to save millions of American lives – five times faster than any other vaccine in history,” White House spokesman Michael Bars said in an email.

Both companies have said they would be ready to distribute a vaccine almost immediately after receiving a green light from the FDA. Results reported last week from a third coronavirus vaccine candidate, from AstraZeneca and the University of Oxford, were positive but confusing, and it is unclear whether that vaccine can move forward in the United States without more data.

The AstraZeneca trial is continuing in the United States, and a single-shot vaccine from Johnson & Johnson is being tested. Novavax, another leading vaccine candidate in the United States, announced Monday that its large U.S. trial, which had been expected to begin this month, would start in the coming weeks.

The full data from Moderna and Pfizer will likely leave some questions unanswered. No one knows yet how long immune protection will last, and it is unclear whether the vaccine will decrease transmission in addition to preventing illness. One worst-case scenario debated by scientists is a vaccine that prevents symptoms and disease but does not decrease the spread of the virus by asymptomatic people.

In its news release Monday, Moderna reported that the vaccine performance was consistent across all ages, races, ethnicities and genders. There were 33 cases of covid-19 in people over 65; 29 cases in people who identified as Hispanic; six cases in Black people; four cases among Asian Americans; and three in multiracial people.

Most reactions to the vaccine were mild or moderate, according to a previous news release from the company. The adverse events rated as “severe” in the trial were soreness at the injection site, tiredness, muscle aches, headache and pain.

“We believe that our vaccine will provide a new and powerful tool that may change the course of this pandemic and help prevent severe disease, hospitalizations and death,” Stéphane Bancel, Moderna’s chief executive, said in a statement.

Moderna will also file for approval from the European Medicines Agency and has an open application with regulators in the United Kingdom, Switzerland, Canada, Israel and Singapore.

Moderna’s vaccine can be stored frozen at minus-20 degrees Celsius and lasts at refrigerator temperatures for up to a month, which probably would make it easier to deploy than the candidate from Pfizer and BioNTech, which requires ultracold storage conditions not typically found at pharmacies and doctors’ offices.