Two COVID-19 vaccines are expected to be evaluated by the Food and Drug Administration soon, raising hopes that pre-pandemic life could resume, but piecing together varying messages from drug companies, experts and the government into one clear timeline isn’t easy.

When can you expect to get a vaccine? How many people could the United States vaccinate per week? It will take a while, and projections differ.

A vaccine won’t blunt the current third wave of cases, hospitalizations and deaths. There won’t be enough supply in time for loved ones besides potentially health care workers to get a shot before the winter holidays, and full protection doesn’t come until a week or two after a second dose.

“There’s been remarkable progress on vaccines, but those aren’t really going to start kicking in as far as reducing risk for most of us for a few more months,” said former FDA Commissioner Mark McClellan, a Duke University regulatory expert.

Pfizer and its partner BioNTech announced that they will submit vaccine data Friday to the FDA for an emergency authorization, the first developers to do so. Another company, Moderna, plans to follow soon.

If everything goes right, the FDA is satisfied with the data, and enough Americans are vaccinated, then normal life could begin to resume in the second half of 2021, according to Anthony Fauci, the country’s top infectious disease expert.

“It will be a gradual process,” Fauci said at a conference Monday. “From January to April, we’ll get it to those people that fall into the high-priority groups.

“By the time you get to April, end of April, May, June, we’ll have the people who are in the general population. If we can vaccinate them, over a period of the second quarter of 2021 and into the third quarter, as we approach the fourth quarter of 2021, I think we can get back to a considerable degree of normality,” he said.

Fauci’s National Institute of Allergy and Infectious Diseases co-developed one of the frontrunner vaccine candidates with the company Moderna.

Internal Centers for Disease Control and Prevention projections assume it could take as long as nine months to vaccinate priority populations, according to estimates made public at an October meeting of outside advisors.

A CDC researcher projected that vaccinating health care workers, essential workers, adults over 65 years old and adults with co-morbid conditions would require 400 million vaccine doses.

Each course requires two doses, with 21 or 28 days in between.

Some information isn’t public, including supply details in the government’s multi-billion-dollar contracts with Moderna and with Pfizer and BioNTech, which have been kept secret even from President-elect Joe Biden and his team. Staff at the Department of Health and Human Services reportedly were told not to communicate with the incoming president’s advisors.

“There’s a lot this administration has said it’s doing, but we do not have visibility into,” said Sen. Patty Murray, D-Wash., ranking member of the Senate committee overseeing health issues.

Number of doses and timing

Vaccinating about 60 to 70 percent of the approximately 333 million U.S. residents — the percentage experts estimate need to be vaccinated in order to significantly curb the spread — would require approximately 400 million to 466 million doses of vaccine.

Federal officials and vaccine developers have been vague about when doses will be available in the U.S., and to what degree their projections could vary depending on manufacturing challenges.

Under the terms of a purchasing agreement with the government, Pfizer and BioNTech would supply the U.S. with 100 million doses, and the government has the option to purchase another 500 million. Moderna has committed to 100 million doses, and the government can buy another 400 million.

It’s not clear how quickly those doses can be made available, and how much of the companies’ global manufacturing capacity will go to the U.S.

“I am confident that if everything goes well, and we have a very organized vaccine supply, that we could have a normal summer and winter 2021,” BioNTech CEO Uğur Şahin told CNN Wednesday.

“Our goal is to supply several hundred million of doses in the first four to five months of 2021, and this will already have an impact in the control of COVID-19,” he said, without specifying how many doses might go to the U.S.

Pfizer did not respond to an email requesting clarification.

More vaccines by other companies could be authorized as soon as the second quarter of 2021, McClellan said, but would need to be proven safe and effective.

Moncef Slaoui, co-leader of the administration’s vaccine and therapeutics effort Operation Warp Speed, said Wednesday that if both the Moderna and the Pfizer vaccines are authorized by FDA, 40 million vaccine doses or more could be available by the end of this year. That would be enough to vaccinate the 20 million health care workers in the U.S., the highest-priority group.

The number of doses could be lower after the company runs safety tests on its manufacturing, said pharmaceutical consultant Norman Baylor, a former director of FDA’s Office of Vaccines Research and Review.

“The manufacturers are making a product they’ve never made before. You can say when you get started: I have all the ingredients, and this is what it’s going to take, and this should equate to 100 million doses. Then you find out, oops, I dropped something, that’s not fit to use anymore. So your projections are tempered,” Baylor said.

Experts say vaccine manufacturing requires a “long runway.”

“It’s not like a pizza that is ready in, start to finish, 20 minutes. It’s months from start to finish of any given lot,” said John Grabenstein, former global executive director of medical affairs for Merck Vaccines and former senior scientist and director for the Pentagon’s immunization program.

It’s not clear how fast vaccine doses can be administered after being manufactured. Distribution challenges include a lack of funding for public health departments, the sensitive cold-chain requirements for the Pfizer vaccine and the potential for wastage.

First in line

A National Academies of Sciences, Engineering and Medicine working group has recommended who should be protected first as doses become available.

Final recommendations about who to prioritize ultimately would come from a group of independent expert advisors to the CDC called the Advisory Committee on Immunization Practices. It will likely meet within 24 hours of any vaccine winning FDA authorization.

States have their own distribution draft plans and do not have to follow the guidance by the National Academies or ACIP. So far, though, states have followed the National Academies’ advice to prioritize medical workers first. Many states also plan to put seniors or those with medical conditions next in line, as the Academies suggested.

Health care workers could be fully vaccinated by late January or February if all goes smoothly.

One obstacle could be that it will be difficult for hospitals to vaccinate their workers given the staffing shortages caused by many falling ill from COVID-19 amid the surge in cases, said Syra Madad, an infectious diseases epidemiologist.

Nursing homes also would get their own separate allocations through a partnership between the government and two major pharmacy chains, CVS and Walgreens. Some experts have raised concerns about how smoothly that allocation will go, because these companies may not have the same institutional knowledge as more specialized pharmacies that typically supply nursing homes.

Next up under the National Academies’ recommendations are people with two or more co-morbid conditions — like asthma, chronic obstructive pulmonary disease, heart disease, kidney disease or diabetes — that put them at a three times greater risk of severe illness from COVID-19.

“Americans who are higher risk — meaning over 60 or 65, with a chronic condition, or who are obese, and that’s a lot of Americans, about half or more — could start to get access in later January, February maybe,” McClellan said.

People with two co-morbid conditions comprise about 10 percent of the U.S. population, or 33 million people, requiring 66 million vaccine doses, according to the National Academies.

Essential workers, another priority group identified by the National Academies, comprise about 80 million Americans, requiring 160 million doses, according to the CDC.

Within each of these priority groups, variations in distribution could be determined by considerations of racial and economic equity. The National Academies recommended using the CDC’s Social Vulnerability Index, which uses Census data to identify vulnerable communities.

The Trump administration left many vaccine distribution questions to states and cities, so whether you are in a priority group will depend on where you live.

“Because each state is almost on their own, they’re developing their own frameworks,” said Madad.

When high-risk groups get a vaccine, it could ease hospital staffing shortages and begin to reduce deaths.

“You will start to see a decline in mortality first, hopefully, before you start seeing a decline in transmission,” said Yale Institute for Global Health Director Saad Omer, a member of the National Academies working group.

But achieving a world where everyone can go to work, restaurants, coffee shops and movie theaters without fear will take longer.

“If we look at our exit strategy out of this pandemic, a vaccine isn’t going to be a panacea,” said Madad. “I think that the media potentially does a disservice when it talks about a timeline, or a particular date. ‘2021, masks will come off and we’ll go back to normal.’ That’s not the case. We need to follow the data, not a date.”