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Doses of the Pfizer-BioNTech COVID-19 vaccine are seen at the Beaumont Service Center, Tuesday, Dec. 15, 2020 in Southfield, Mich. (AP Photo/Carlos Osorio) Doses of the Pfizer-BioNTech COVID-19 vaccine are seen at the Beaumont Service Center, Tuesday, Dec. 15, 2020 in Southfield, Mich. (AP Photo/Carlos Osorio)

Doses of the Pfizer-BioNTech COVID-19 vaccine are seen at the Beaumont Service Center, Tuesday, Dec. 15, 2020 in Southfield, Mich. (AP Photo/Carlos Osorio)

Samantha Putterman
By Samantha Putterman December 17, 2020

If Your Time is short

  • The new COVID-19 vaccines, which officials say will be free, are expected to become available to the general U.S. population in the spring and summer of 2021.

  • The Pfizer and Moderna vaccines use a new and well-researched technology, called mRNA, which gives the body instructions to produce copies of the protein present on the surface of the virus without causing sickness from the disease. The immune system then learns to recognize it and produce antibodies against it.

  • The vaccines have been shown to cause mild or moderate short-term reactions that resolve without complication. 

The distribution of coronavirus vaccines begins a hopeful new phase of the pandemic, but most Americans will have to wait.

The first doses are going to health care workers and at-risk populations. It may take until the spring or summer months, at the earliest, for the general population to receive their shots.

Some parts of the process should feel normal. Officials say vaccines will be free for Americans, even if they don’t have health insurance. And they will likely be scheduled through doctor’s offices and pharmacies like CVS and Walgreens, similar to the way people receive the annual flu shot. A lot could still change depending on which vaccines are approved. 

This guide presents some key facts about the vaccines — as well as some unknowns. The reporting comes from our vaccine fact-checks, our responses to reader questions, and a Poynter Institute seminar with vaccine experts.

8 facts about the new vaccines

1. The vaccines, while developed quickly, rely on scientific research that goes back decades.

The first two coronavirus vaccines from Pfizer and Moderna were developed in record time and use new technology, called messenger RNA, to combat the disease.

But that does not mean that safety protocols were bypassed or that researchers didn’t do enough testing. The research behind the new vaccine technology has been underway for some time. 

"It's not a novel strategy," said Dr. Paul Offit, director of the Vaccine Education Center at Children’s Hospital of Philadelphia. "This particular notion of using messenger RNA in a vaccine has been around for 20 years. This is just the first product to get above the water to become a commercial project."

Traditional vaccines introduce an inactivated or weakened version of a virus for the body to fight against. By contrast, COVID-19 vaccines from Pfizer-BioNTech and Moderna use messenger RNA, which is a fragment of the virus’ genetic material. 

It works by giving the body instructions to produce copies of the protein present on the surface of the coronavirus, without causing sickness from the disease. The immune system then learns to recognize and produce antibodies against the protein.

2. The vaccines are considered safe.

There was a rigorous review process. 

For example, the vaccine developed by Pfizer-BioNTech has been studied in clinical trials involving about 44,000 people, with half receiving the vaccine, and the other half receiving a placebo. To receive emergency use authorization from the FDA, the manufacturers had to follow at least half of the participants for at least two months after their vaccinations, and the vaccine had to be proven safe and effective in that population.

An FDA analysis of that vaccine’s data found "no specific safety concerns" that would rule out using it for people aged 16 and older. 

3. You may feel crummy after receiving a shot, but most side effects are mild or moderate.

People who have received the top COVID-19 vaccine candidates have reported mild or moderate reactions, such as fatigue, headache, some arm soreness or a fever. They usually resolve without complications in a day or two.

"If you have some sort of reaction, that means the shot is actually working," said Dr. Patricia A. Stinchfield, a pediatric nurse practitioner and president-elect of the National Foundation for Infectious Diseases. 

"Your immune system is responding. It sees the bad guy, and it’s making the good guys," she said. "It’s a small, one- to two-day sense of illness, and it is far, far better than having COVID disease."

4. The federal government won’t mandate it.

Neither the Trump administration nor the incoming Biden administration has announced plans to make the vaccine mandatory. In several interviews, Biden has taken an unequivocal stance against requiring it.

Dr. Anthony Fauci, the director of the National Institute of Allergy and Infectious Diseases and a member of the White House Coronavirus Task Force, said a federal mandate would be "unenforceable and not appropriate."

"You don't want to mandate and try and force anyone to take a vaccine," Fauci said in August, "We’ve never done that. You can mandate certain groups of people, like health care workers, but for the general population you can’t."

States have the general authority, within constitutional limits, to enact laws requiring vaccination. All 50 states and the District of Columbia, for example, have laws requiring certain vaccines for students, with some exemptions. 

5. It does not affect human DNA.

The genetic material in the vaccine candidates, called messenger RNA, or mRNA, doesn’t alter the DNA of a human cell.

The mRNA "never enters the nucleus of the cell and does not affect or interact with a person’s DNA," the Centers for Disease Control and Prevention says on its website.

Converting RNA into DNA isn’t possible outside of a special enzyme contained on some viruses, and COVID-19 isn’t one of them, Brent Stockwell, a professor at Columbia University who studies cell and molecular biology, told PolitiFact.

"So there is no obvious mechanism by which a person’s DNA could be altered by an mRNA vaccine," he said. 

6. If you’ve had adverse reactions to vaccines before, talk to your doctor first. 

The CDC says that clinical trials demonstrated that the Pfizer vaccine would be effective and safe for those with underlying medical conditions, and is especially important for those who are at an increased risk for severe COVID-19.

The vaccine is not recommended for those who have had a severe allergic reaction to an injectable product in the past, but it’s OK for people with other types of severe allergies, as long as they take precautions.

"So, for example, people commonly have peanut allergies, or egg allergies, or other food allergies, you still can get this vaccine," said Offit. "You just need to wait for 30 minutes in the area where you’ve gotten that vaccine so, if you do have an allergic reaction, somebody will be able to give you a shot of epinephrine to reverse it."

For everyone else, health officials recommend hanging around for about 15 minutes following inoculation to make sure you don’t have a reaction.

Two health care workers at Bartlett Regional Hospital in Juneau, Alaska, experienced severe allergic reactions to the Pfizer vaccine. One had to be hospitalized and the other’s symptoms were resolved within an hour.

The reactions are believed to be similar to the anaphylactic reactions that two health workers, who had a history of allergies, experienced after receiving the vaccine in the United Kingdom. All have recovered.

Meanwhile, Offit said that typically, only about one out of every million doses of vaccine is complicated by a severe allergic reaction. Health officials said that the cases would not disrupt their vaccine rollout plans.

7. People who had COVID-19 should get a vaccine.

Medical researchers and immunology experts say it’s rare, but possible, for recovered COVID-19 patients to become infected with the virus again as their natural antibody levels wane over time. The vaccine is expected to provide stronger and likely longer-lasting immunity.

8. You need both doses to be adequately protected.

Both Pfizer and Moderna’s vaccines require two doses for full protection. The efficacy of a single dose has not been evaluated in clinical trials.

The doses for Pfizer’s vaccine are given three weeks apart, with a four-day grace period considered valid. If more than 21 days has passed since the first dose, the CDC says that the second should be administered "at the earliest opportunity," but no doses need to be repeated.

Moderna's vaccine was studied with the two doses coming 28 days apart.

"It’s optimal you get two. You may get some protection from one, but not complete," said Dr. Susan Bailey, the president of the American Medical Association. "We’ve had boosters within immunizations since we’ve had vaccines (and) we know that getting a booster improves your level of immunity."

Researchers say recipients of the Pfizer vaccine will have full protection approximately seven days after the second dose. 

4 unknowns about the vaccines

1. Could the virus mutate like the flu, requiring a new vaccine every year?

The novel coronavirus is a single-strand RNA virus, like measles, mumps and influenza. Offit, who also sits on the FDA’s vaccine advisory committee, said he believes vaccine immunity from COVID-19 will last years, but not necessarily decades. 

"(Will it behave) like influenza, which changes too much in a year, thus requiring a new vaccine each year?" Offit said. "Or is it going to be like measles? Which mutates, but not rapidly."

Researchers expect to know more by mid-2021 about how long vaccine-induced immunity is going to last. At that point, more long-term results from vaccine trials will be available.

2. Could a vaccinated person still spread the virus?

The vaccine isn’t necessarily a silver bullet, medical experts caution, and a safe return to "normal life" may take a while. There’s still not enough data to indicate whether someone could still spread the virus, asymptomatically, after getting vaccinated.

People who receive the vaccine should continue to wear a mask and practice social distancing, experts say.

"It’s risky to assume once you get the shot in the arm that you can live life as normal," Bailey said.

3. Is the vaccine safe for pregnant women?

The vaccines so far have not been tested on pregnant women. Offit said pregnant women should still consider getting the vaccine, because the virus can affect them severely.

"There’s no biological reason to think it would be damaging to pregnant women or to their unborn child," he added.

In its recently released vaccine recommendations, the CDC says that if a pregnant woman is part of a group recommended to receive a COVID-19 vaccine — a health care worker, or a grocery store employee, for example — she may choose to be vaccinated, and that a discussion with her doctor can help her make an informed decision.

We recently debunked false claims that said the new mRNA vaccines will cause infertility in women by harming the placenta. If that effect were true in the way these posts describe, so would having COVID-19 itself, and there’s been no evidence of a link to infertility or pregnancy miscarriages so far.

4. When will a vaccine be available for children?

Young children haven't been a part of any early vaccine trials. Testing began in October 2020 in children as young as 12 for the Pfizer vaccine, and the research is expected to take several more months.

Generally, children don’t experience severe complications from COVID-19. Doctors say it’s critical to get adequate data before vaccinating children. 

Read more:

Alternative health website spreads false claim about COVID-19 vaccine side effects

Ask PolitiFact: Do you have to get the vaccine if you’ve had COVID-19?

No, chip on COVID-19 vaccine syringes would not be injected or track people

Two vaccine trial participants died, but the FDA didn’t connect their deaths to the vaccine

Conspiracy theory targets first recipient of UK COVID-19 vaccine as crisis actor

Fact-checking Facebook post comparing COVID-19 vaccine research to HIV, cancer, common cold

Social media post falsely claims a federal law would require vaccination against COVID-19 

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Our Sources, Reporting on the COVID-19 Vaccines, Dec. 14, 2020

PolitiFact, Ask PolitiFact: Do you have to get the vaccine if you’ve had COVID-19?, Dec. 7, 2020 

Washington Post, 8 facts about the coronavirus to combat common misinformation, Dec. 4, 2020


Food and Drug Administration, Vaccines and Related Biological Products Advisory Committee Meeting, Dec. 10, 2020 

PolitiFact, The COVID-19 vaccine is here. What journalists need to know, Dec. 15, 2020 

New York Times, Answers to Your Questions About the New Covid Vaccines in the U.S., Dec. 14, 2020 

New York Times, No, there isn’t evidence that Pfizer’s vaccine causes infertility., Dec. 10, 2020 

Associated Press, Will children be able to get COVID-19 vaccines?, Dec. 17, 2020 

PolitiFact, No, Pfizer’s head of research didn’t say the COVID-19 vaccine will make women infertile, Dec. 10, 2020 

Centers for Disease Control and Prevention, Understanding and Explaining mRNA COVID-19 Vaccines, Nov. 24, 2020 

Centers for Disease Control and Prevention, Use of Pfizer-BioNTech COVID-19 Vaccine: Clinical Considerations, Dec. 12, 2020

PolitiFact, Alternative health website spreads false claim about COVID-19 vaccine side effects, Dec. 6, 2020

Food and Drug Administration, CBER Plans for Monitoring COVID-19 Vaccine Safety and Effectiveness, Oct. 22, 2020

Mayo Clinic, COVID-19 vaccine myths debunked, Dec. 8, 2020, Debunking COVID-19 vaccine myths, Dec. 9, 2020, 8 coronavirus vaccine myths, debunked, Dec. 7, 2020

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