Pfizer-BioNTech's COVID-19 vaccine has been tested for safety and efficacy in more than 44,000 people. Still, stopping viral spread will take more than immunizations, says the CDC. The agency is calling for those who are vaccinated to continue wearing masks and practicing safe physical distancing.

Pfizer-BioNTech's COVID-19 vaccine has been tested for safety and efficacy in more than 44,000 people. Still, stopping viral spread will take more than immunizations, says the CDC. The agency is calling for those who are vaccinated to continue wearing masks and practicing safe physical distancing. / AP

Updated at 12:26 p.m. ET, Tuesday, Dec. 15

Now that the Food and Drug Administration has issued an emergency authorization for the first COVID-19 vaccine to be deployed over the next few days in the U.S., you may have a lot of questions about what this means for you and the people you love. Here's what we know so far:

Who specifically is eligible for the vaccine now?

With more than 2,300 deaths now routinely linked to the coronavirus in the U.S. each day, getting a safe vaccine into people's arms has been an urgent priority. The FDA late Friday issued an emergency use authorization for the vaccine made by Pfizer and German biotech firm BioNTech to be given to people ages 16 and older.

Is the vaccine safe?

Pfizer has run tests that include more than 44,000 people. An FDA analysis of the vaccine's safety and effectiveness on people aged 16 and older found "no specific safety concerns" that would preclude the vaccine's use. Some mild to moderate side effects are common — mostly swelling, pain, redness at the injection site, fatigue and sometimes including fever that resolves within about 24 hours.

I'm not high risk or an essential worker, so how soon can I get vaccinated?

Not for a while. The Department of Health and Human Services expects to send about 2.9 million doses out in the first push this week. Those doses are to be divvied up among states based on their population. Last week, Secretary of Health and Human Services Alex Azar promised that the government would provide enough vaccine for 20 million Americans before the end of the year and says there should be enough for everyone in the U.S. in the spring — likely not just the Pfizer vaccine but also others that are still in the research pipeline.

The Centers for Disease Control and Prevention has endorsed a plan to prioritize the nation's 21 million health care workers and 3 million residents of long-term care facilities. States have the final say over which groups are first in line for any vaccine the federal government sends them, but they are expected to go along with the CDC recommendation. After those two groups, vaccine is likely to go to the 87 essential million workers not involved in front-line health care, then to the 100 million adults with certain high-risk medical conditions and the 50 million people who are 65 years old or older.

If there are a few different vaccines coming, which one is best for me?

Right now, you don't have much choice. Only the Pfizer vaccine has been granted emergency authorization for use. A vaccine that works in similar ways made by Moderna is expected to get that authorization, too — perhaps as soon as this week. Measures of the safety and effectiveness of the two vaccines seem roughly comparable.

Other vaccines under development use different approaches to the same end. One relies on a harmless virus loaded with a coronavirus gene for a protein that will induce an immune response, and several companies are working on more traditional, weakened-virus vaccines.

Some of the candidate vaccines are single-dose, while others (specifically Pfizer's and Moderna's) require two shots, spaced three to four weeks apart for full protection. Some of the vaccines must be kept extremely cold.

Dr. Marisa Holubar, an infectious disease physician at Stanford University, tells NPR, "I think there will be likely some subpopulations in which one vaccine might be better than the other."

The FDA guidelines to prescribers, issued Friday, note only that "immunocompromised persons, including individuals receiving immunosuppressant therapy, may have a diminished immune response" to the Pfizer vaccine.

As more vaccines are evaluated, Holubar says, it may turn out, for example, that elderly people with weakened immune systems might be more responsive to one type of vaccine over another. A detailed FDA analysis of the Moderna vaccine released Dec. 11 found that for people ages 18 to 64, the effectiveness is 96%, compared with 86% for people 65 and older.

It might also turn out that a company decided not to test a subgroup — say, children under 12 — but another manufacturer did.

Data on which to base decisions about whether some vaccines are better for different groups are still emerging. And some people might opt for a single-dose type of vaccine for logistical reasons, she notes.

Where will I be able to get the vaccine?

Many doses of Pfizer's vaccine have already been deployed to the company's hubs in the U.S. and will now be shipped across the U.S. According to Operation Warp Speed, the vaccines will be picked up from manufacturers by UPS, FedEx and medical supply company McKesson for delivery to pharmacies, nursing homes, public clinics, hospitals, doctors' offices, mobile clinics and military facilities.

Initially, states are likely to direct first supplies to larger distribution centers — such as hospitals and long-term care facilities. The drugstore chains CVS and Walgreens are responsible for delivering the vaccine to nursing homes, which are likely also to be among the first places for availability.

States will be in control. You can check out what your state has been planning on Page 25 of this document on vaccine distribution from Duke University and the National Governors Association.

What side effects can I expect from the vaccines?

In the Pfizer and Moderna trials (which included an average of two months of follow-up), vaccine recipients have reported mild symptoms (such as sore arms, redness at the injection site, headache or fatigue) a little more frequently than with flu vaccines, says Dr. Paul Offit, a pediatrician at the Children's Hospital of Philadelphia and a member of the FDA's advisory committee evaluating the vaccines. Offit says mild to moderate symptoms — similar to the range of side effects seen with the shingles vaccine Shingrix — are to be expected, and people need to understand that.

Vaccine recipients, especially under age 65, "could have fever — including rarely high fever — fatigue, headaches, chills, muscle aches, joint pain, enough so that one could miss a day of work," Offit tells NPR. (Pain at the injection site and fever were apparently more common in the Moderna research trials, than in Pfizer's — reported by 91% of those immunized.)

"But that's just your immune system being vigorous and working for you," Offit says. "In many ways, it's a good thing. But you can't have people surprised by this because it is actually a fairly common problem."

An FDA-posted fact sheet and prescribing instructions regarding the Pfizer vaccine reports that in one trial, 0.4% of people who had gotten the vaccine had a serious adverse event compared with 0.3% of those who received a placebo. A New England Journal of Medicine report published this week described the incidence of serious adverse events as "low, and similar in both groups."

In the United Kingdom, which began vaccinating with the Pfizer vaccine last week, there have been two or three cases of strong allergic reactions in people who have a significant enough history of severe allergies that at least two routinely carry EpiPens. The reaction was safely quashed with a shot of epinephrine.

The fact sheet the FDA posted advises health workers to not give the Pfizer vaccine to "individuals with known history of a severe allergic reaction (e.g., anaphylaxis) to any component of the Pfizer-BioNTech COVID-19 Vaccine." The agency noted in a press briefing Saturday that the warning does not extend to the 1.6% of people who have had a severe allergic reaction to foods or something in the environment.

Both the Pfizer and Moderna vaccines are based on a new model — getting genetic material into people's cells so that the cells produce proteins that will trigger an immune reaction. "There's no particular reason based on the science to be concerned about long-term side effects," says Dr. Jesse Goodman, former FDA chief scientist and now at Georgetown University. "But that said, careful monitoring over time will be needed."

I'm pregnant. What should I do about getting immunized?

Many vaccines are safe and effective and are recommended for pregnant women, but pregnant women were excluded from both the Moderna and Pfizer studies, so no one can say for sure how the vaccine will perform in this group. Several studies have shown that pregnant women who get COVID-19 are more likely to have a worse run of it, so it would be helpful to have more data.

"We think and hope the vaccines will be useful and safe for pregnant women," says Goodman. "But we need the studies."

The issue came up during the advisory meeting Thursday, and Pfizer said it would be releasing results on toxicity studies in rats soon. The FDA's guidance did not preclude offering the vaccine to pregnant women, but experts say there isn't enough information to assess the risks versus benefits in a way that would merit blanket advice.

Dr. Denise Jamieson, chair of the Department of Gynecology and Obstetrics at Emory University School of Medicine, tells NPR's Laurel Wamsley that because one side effect of the shot can be fever — "something that we try and avoid in pregnancy — it may be important that if [vaccinated] women get a fever, that they treat it with acetaminophen."

Beyond that, Jamieson suggests, watch for further guidance as more research emerges and check with your doctor about your particular circumstances in the meantime.

What about kids?

Participants in Pfizer's vaccine studies were mostly adults, and the FDA's authorization is for people 16 and older. So far, only 163 people in Pfizer's 44,000-person trial were as young as 16 or 17, notes Dr. Cody Meissner in an interview with NPR. He is chief of pediatrics at Tufts University Medical Center and one of the FDA advisory committee members. Half of that group got the placebo, and none of the participants in the research trial was younger than 16, Meissner notes. The American Academy of Pediatrics is calling for adding younger people to the vaccine clinical trials.

The FDA's Dr. Peter Marks, director of the Center for Biologics Evaluation and Research, notes that many 16- and 17-year-olds are working as checkout workers or are otherwise active in their communities, so their risk of contracting the coronavirus can be elevated. "We think the known and potential benefits outweigh the known and potential risks" of immunizing this age group, he says.

If I get vaccinated, can I go back to life as normal?

No, not right away. Studies of the new vaccines only measured whether vaccinated people developed symptoms, not whether they got infected. It's possible that they got light infections — not enough to make them ill, but enough to pass the virus on to others. "That's why I tell people when you get vaccinated, continue wearing your mask," Dr. Carlos Del Rio, a vaccine scientist at Emory University who helped test the Moderna vaccine, recently told NPR. "We're going to know later if the vaccine actually prevents infection."

The CDC is calling for those who are immunized to continue wearing masks and practicing safe physical distancing until more is learned. "Experts need to understand more about the protection that COVID-19 vaccines provide before deciding to change recommendations," as well as how many people are getting vaccinated and whether the virus is still spreading in communities, it says in an FAQ.

My mom got her first dose and I want to visit. Are there still safety issues?

Yes — remember, both doses are necessary for full effectiveness. And for now at least, you should take the same precautions you did before vaccination, says Goodman. "Until the population is broadly vaccinated and the outbreak under control, which will take many months, everyone — vaccinated or not — needs to continue to wear masks and practice distancing to protect themselves and others."

If I've had COVID-19, should I get vaccinated anyway?

It looks like getting vaccinated when you've been infected in the past is safe — in both the Pfizer and Moderna trials, about 5% to 10% of volunteers turned out to have already been infected. And many experts say the extra protection of immunization might be helpful. But the CDC is waiting until there is more information about how long "natural immunity" lasts to give advice about that.

How much will getting immunized cost me?

The government will be providing vaccines for free, but providers will be allowed to charge a fee for giving the shots. They can recoup the fee from public and private insurance plans and from a government fund to cover uninsured individuals.

Will I need a booster shot?

Some of the vaccines further down the pipeline are single shots, but the Moderna and Pfizer vaccines require two doses to hit the 94% or 95% effectiveness level. With other multidose vaccines, people often miss the second shot. Researchers say they hope that a prior awareness that some mild or moderate side effects are likely will make people less leery of a second shot and that clear messaging about the importance of full vaccination will bring people back. Additional boosters may be necessary in upcoming years — the current vaccines have been tested only over a period of six months, and it is possible immunity could wane.

Is it safe to send kids back to schools?

It likely will be awhile before any of the COVID-19 vaccines are authorized for use in children — the early vaccines have not been tested in kids under 16. And it's going to take a long time for vaccination to lower the overall rate of infection in the community and thus lower the likelihood of the coronavirus coming into the schools from outside. Infectious disease experts say that for now, the safety of the youngest students has much more to do with whether their school makes sure that students, faculty and staff keep properly distanced and wear masks where appropriate; provides washing-up areas; and ensures good ventilation.

"We know that the vaccine's been given to tens of thousands of people safely," Offit tells NPR regarding the Pfizer vaccine. "So we can say, at least with comfort, that it doesn't cause an uncommon, serious side effect. And that doesn't mean it doesn't cause a very rare serious side effect. We'll find that out post-approval. But I think we know enough. When you agree to move forward with a product, it's not whether you know everything. It's whether you know enough to say that the benefits outweigh what at this point are theoretical risks."

Joanne Silberner, a former health policy correspondent for NPR, is a freelance journalist living in Seattle.

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