Your questions about coronavirus vaccines, answered

Updated Feb. 2 at 10:58 p.m.

The first coronavirus vaccine was administered to U.S. health-care workers Dec. 14. Now that a second vaccine is being used, public health officials are hoping that as much as 85 percent of the population will be inoculated so that the nation can achieve herd immunity and stop the virus’s spread. Here are answers to some frequent questions.

What you need to know about the vaccines

chevron-rightHow do the Pfizer-BioNTech and Moderna vaccines work?

The first vaccine authorized in the United States was developed by pharmaceutical giant Pfizer and the German firm BioNTech. It consists of two shots, given three weeks apart. Moderna’s vaccine, developed by a Massachusetts biotechnology company in partnership with the National Institute of Allergy and Infectious Diseases, was the second vaccine cleared. It consists of two shots, given 28 days apart.

The Pfizer-BioNTech and Moderna shots are the first vaccines using messenger RNA technology approved for human use by the Food and Drug Administration. The approach is different from that of more traditional vaccines, which often use a weakened or dead version of a virus, or a laboratory-generated protein. It uses a synthesized scrap of genetic information that is wrapped in a protective fat layer to keep it from disintegrating. When it goes into cells in the muscle of the upper arm, it contains molecular instructions that tell your cells to create a protein that triggers an immune response to the spike protein on the surface of the coronavirus. This means your immune system will be prepared to eliminate the pathogen if it tries to invade.

chevron-rightAre they safe?

Both vaccines passed rigorous safety reviews by the FDA.

The agency authorized the Pfizer-BioNTech vaccine for people age 16 and over after reviewing data from 44,000 participants in a randomized clinical trial. A 53-page analysis by the agency found that some people who received injections had unpleasant but tolerable side effects, including fatigue, headaches, muscle pain, joint pain, chills and fever. Reviewers said the two months of follow-up on 38,000 of those participants provide evidence of “a favorable safety profile, with no specific safety concerns identified that would preclude issuance of an [emergency authorization].”

The FDA cleared the Moderna vaccine for people age 18 and over, based on data from a clinical trial with 30,000 participants. The agency found side effects were similar to those with the Pfizer-BioNTech shot.

Some experts have expressed qualms about using emergency use authorizations for coronavirus vaccines that would be given to hundreds of millions of people, but those criticisms have become muted as the pandemic has raged, killing thousands of Americans a week.

Peter Marks, director of the FDA center that oversees vaccines, has vowed to use an emergency standard roughly equivalent to what’s needed for a full licensure. Even so, the available safety data — two months of follow-up on half the trials’ participants after their second shots — is shorter than in traditional trials. And some questions, such as the duration of protection, can’t be answered now. That data will be collected as the trials continue.

chevron-rightWill the vaccine protect me from getting the coronavirus?

The two-shot Pfizer-BioNTech vaccine has been shown to be 95 percent effective in randomized trials. The FDA’s independent review found that of more than 20,000 people who received both vaccine doses, only eight contracted the coronavirus, and just one person fell seriously ill. By contrast, 162 people in the placebo group contracted the coronavirus, and nine of those people developed serious illness. There was even some evidence that the first shot of the vaccine protected against illness, but the FDA said there was insufficient data to draw firm conclusions.

Moderna’s vaccine was found to be 94 percent effective at preventing disease in the trial, and particularly effective against severe disease.

Scientists don’t yet know how long the protection from the vaccines last. And they don’t know whether the shots prevent people from becoming infected without knowing it and inadvertently spreading the virus.

chevron-rightHow effective are they against the new coronavirus variants? If I’m vaccinated now, will I have to get another shot to protect against those?

The experts don’t know yet. Scientists think the Moderna and BioNTech vaccines will still work against two variants of concern that were first identified in the United Kingdom and South Africa, but emerging evidence — including from a different experimental vaccine trial — suggests that the protection might be considerably less complete.

Vaccine companies are already working on revising vaccines so that they could be deployed to block the variant of greatest concern, which was first identified in South Africa, if needed. Moderna has announced it would develop and test a new vaccine as well as a third dose of its current vaccine to see if it protects people better against emerging variants.

chevron-rightHow were the vaccines made so fast?

Historically, vaccines have taken years to develop. Before these, the mumps vaccine — which took four years to develop — was the fastest to be approved for use in humans. Developing messenger RNA vaccines such as the Pfizer-BioNTech and Moderna candidates has been fast because scientists were able to start their work before there was a known case of the novel coronavirus in this country, using the viral genome shared online as a template. Making messenger RNA vaccines does not require time-consuming steps, such as growing ingredients in chicken eggs.

chevron-rightWhat’s happening with vaccines from Johnson & Johnson, Oxford-AstraZeneca and Novavax?

Johnson & Johnson has a single-shot vaccine that appears headed for authorization in the United States after a global trial showed it was robustly effective at preventing illness, hospitalizations and death. No serious side effects were reported in the study. The results put a third vaccine on the horizon in the United States — one with logistical advantages that could simplify distribution and expand access to shots worldwide. The shot could be authorized by the Food and Drug Administration and available to the public by March.

The European Union’s regulator has recommended authorization of a coronavirus vaccine from Oxford-AstraZeneca for use in the 27-country bloc, despite a lack of data about efficacy in older people. European officials had raised concern about the limited knowledge of the vaccine’s effectiveness in older people, who represented only 6 percent of clinical trial participants, though they account for most coronavirus deaths and are high on most countries’ vaccination priority lists. The United States is waiting for further trial data before authorization, and Germany announced Thursday that it would recommend that the vaccine only be used in adults under 65.

A coronavirus vaccine made by Maryland biotech company Novavax — which is in the midst of a large late-stage trial in North America — proved effective at stopping symptomatic infections in global hot spots where concerning variants are dominant, the company announced Thursday. But warning signs lurked amid those findings: The protective effect of the vaccine was substantially muted in South Africa, where a worrisome virus variant is in wide circulation.

Should I still get vaccinated if …

chevron-rightI already had the coronavirus?

The Centers for Disease Control and Prevention says vaccination should be offered to people regardless of whether they had a prior infection. We are still learning how long immunity to the coronavirus lasts, after an infection or a vaccination. Typically, an infection causes better immunity than a vaccine, but not always — the vaccines for tetanus and human papillomavirus, for example, offer better protection than recovering from a natural infection.

chevron-rightI have covid-19 now?

It’s best to wait to be inoculated until you’ve recovered from your illness and have met all the criteria to end self-isolation to avoid spreading the infection to others. There is no recommended minimum interval to get vaccinated after you’ve recovered.

chevron-rightI’m pregnant, plan to get pregnant soon or I’m breastfeeding?

Pregnant or breastfeeding people who are part of a group recommended to get the shots — for instance, health-care workers — might want to consider talking with their medical providers beforehand. Pregnant people have been excluded from coronavirus vaccine trials, so there is no data on the safety of the vaccines for them, or its effects on the breastfed infant.

The American College of Obstetricians and Gynecologists says a conversation with a clinician may be helpful but should not be required. Pregnant people who get infected with the coronavirus are at greater risk of death and severe illness than those who are not pregnant, even as the overall risk remains small.

The Pfizer-BioNTech and Moderna vaccines do not contain live virus, or any enhancers to boost an immune response, and are not thought to be a risk to the breastfeeding infant. They do not alter human DNA in the people who get it and cannot cause any genetic changes. Also, this type of vaccine breaks down quickly and doesn’t enter the nucleus of the cell.

Pfizer said it is planning to report to the FDA by the end of the year on a developmental and reproductive toxicity study in animals that could help clarify any risks.

chevron-rightI have allergies?

People who have mild allergies to food, pets, environment or latex can get the Pfizer-BioNTech and Moderna vaccines.

Concerns about rare but severe allergic reactions were sparked by recent reports that two health-care workers in Britain had such reactions after being vaccinated. The CDC said Dec. 19 that it was reviewing six cases of anaphylaxis in people given the Pfizer-BioNTech vaccine.

Government officials and medical experts say these rare reactions should not deter the general public from taking the vaccine, although the standard guidance is that people who get the shot should linger at the clinic or doctor’s office for 15 minutes, and 30 minutes if they have a history of severe allergic reactions. Anaphylaxis can be quickly reversed with epinephrine and other medicines.

The FDA and the CDC say people with a history of severe allergic reactions to any component of the vaccines should not get the shots.

Researchers do not know which component in the Pfizer-BioNTech vaccine might have triggered the severe allergic responses. Many, but not all, of the chemicals in that shot and the Moderna one are the same. They both use polyethylene glycol, a chemical widely used in medicines, cosmetics and other household products, which the FDA has said it is looking at as a possible culprit. Officials at the National Institutes of Health are devising a study to find out why a small number of people have had severe allergic reactions to the Pfizer-BioNTech vaccine.

If you have a history of severe allergic reaction to another vaccine or injectable therapy, that should not necessarily preclude you from getting the shots. But the CDC advises that you consult your doctor beforehand.

chevron-rightWhat about people with HIV infections or who have other immunocompromising conditions, or who take immunosuppressive medications?

The vaccines haven’t been studied in immunocompromised people, but those individuals are not anticipated to be at increased risk of adverse reactions. However, they should talk to their providers beforehand because their immune systems may not respond optimally.

I want to get the vaccine …

chevron-rightWhen will I be able to get vaccinated?

That depends on your job, your age and your health. For the most up-to-date information, see The Washington Post’s vaccine distribution tracker.

A CDC advisory committee has said the first group to receive the vaccines should be health-care workers and residents of long-term care facilities. States, however, have the final say. Government officials had said they anticipated having enough doses of the two vaccines to inoculate 20 million people with their first shots by the end of 2020 — a goal they failed to reach.

The next priority group for the vaccines should be essential workers — grocery store employees, teachers, emergency workers and others who are on the front lines of the nation’s labor force — and adults 75 years old and older, the CDC advisory panel said. Those groups could get shots early in 2021.

A third group that should get priority includes other essential workers, adults 65 to 74 and people 16 to 64 with high-risk medical conditions, the committee advised.

Who exactly is an “essential worker” already is setting off debate around the country. Complicating the situation: There will not be enough vaccine to meet demand any time soon.

Healthy younger adults who don’t have medical conditions or high-risk jobs are likely to begin to get vaccinated starting in April, but not everyone will be able to get the shots immediately. And children aren’t even included in most coronavirus vaccine trials — Pfizer is the first company to expand its trial to people 12 and older — so they probably will be among the last to get access.

“I would say starting in April, May, June, July — as we get into the late spring and early summer — that people in the so-called general population, who do not have underlying conditions or other designations that would make them priority, could get” shots, said Anthony S. Fauci, director of the National Institute of Allergy and Infectious Diseases.

chevron-rightBut there must be some things I can do that I couldn’t do before?

Public health experts say people who have been vaccinated can enjoy a bit more freedom — for example, flying while masked is far less of a risk after inoculation, as is going to the grocery store or getting a haircut. And some say it’s okay to get together, carefully, with other inoculated people.

“For those who have really been like hermits and living under a shell, I think being vaccinated gives you the confidence to maybe go out to a store, go out to a restaurant while observing the public health precautions,” said Onyema Ogbuagu, principal investigator for Pfizer’s vaccine trial at Yale University. “Being vaccinated gives you that extra confidence that I can still go places, still maintain distance, but still go places.”

Some experts are more conservative, advising people to avoid indoor dining or gather even with the vaccinated until the United States achieves herd immunity, in which 70 to 85 percent of Americans are protected from the virus because they have been vaccinated or previously had covid-19. That should prevent the virus from circulating freely, but could be many months away.

For people who have been vaccinated, getting together with other inoculated people is much safer than before, said Paul Sax, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital in Boston. “The only thing that people want to hear, though, is, ‘Is it 100 percent safe?’ And we don’t have proof of that yet.”

chevron-rightHow will the vaccines be shipped?

The vaccine from Pfizer and BioNTech must be kept at an ultracold, minus-70 degrees Celsius, a requirement that will add a wrinkle to an unprecedented vaccination campaign. The company has created its own GPS-tracked coolers filled with dry ice to distribute it.

Each vial of the Pfizer vaccine holds five doses when diluted. Once thawed, the undiluted vial can be kept in a refrigerator for only five days. A diluted vial can be kept for only six hours before it must be discarded.

The Moderna vaccine is stored frozen at minus-20 degrees Celsius, but it keeps for a month at refrigerator temperatures. This could make it easier to distribute to pharmacies and rural areas that don’t have specialized freezers.

chevron-rightHow much will the vaccines cost?

The federal government has pre-purchased hundreds of millions of vaccine doses with taxpayer money, and vowed to make them available free.

chevron-rightWill I have a choice on which vaccine to take, assuming more than one is approved?

Supply will be far short of demand initially, so you are unlikely to be offered options in the near term. Also, the vaccines have different storage and handling requirements, making it likely that each administration site will have only one vaccine on hand, at least to start with.

But Kelly Moore of the Immunization Action Coalition believes that once plenty of products are available, that may change. Moore hopes supply may meet demand by the second half of next year, opening the potential for people to have options, particularly if one vaccine is preferable for certain age groups, for example.

What can I do after I get vaccinated?

chevron-rightCan I return to my old activities?

Not at first. Public health experts say in the short term, life will look much the same after you get vaccinated, until a larger share of the population is vaccinated and the pandemic is curbed. For the most part, they recommend that people still wear masks, maintain their distance around those not in their household, especially if they are unvaccinated.

One reason for caution is that the vaccines currently in use are 95 percent – but not 100 percent – effective at preventing covid-19 from the original strain of the coronavirus they were tested against but may confer less protection against newer variants, first identified in South Africa and Brazil, and now circulating in the United States. So there is a small possibility people who are vaccinated could get sick, though it is very unlikely they would be hospitalized or die.

For the next several months, some people will be vaccinated and many will not, and it’s important to protect those who must wait for their shots. Scientists haven’t ruled out the possibility that people who have been inoculated can transmit the virus to the unvaccinated. They are hoping to have data on that issue in the next few months and, if it shows that vaccinated people can’t be carriers, that could lead to more relaxed interactions.

Chris Alcantara, Sarah Kaplan, Christopher Rowland and Frances Stead Sellers contributed to this report.

Carolyn Johnson is a science reporter. She previously covered the business of health and the affordability of health care to consumers.
Aaron Steckelberg is a senior graphics editor who creates maps, charts and diagrams that provide greater depth and context to stories over a wide range of topics. He has worked at the Post since 2016.
Lena H. Sun is a national reporter for The Washington Post covering health with a special focus on public health and infectious disease. A longtime reporter at The Post, she has covered the Metro transit system, immigration, education and was a Beijing bureau chief.
Laurie McGinley covers health and medicine for The Washington Post. She focuses on the Food and Drug Administration as well as cancer research and treatment. She was previously The Post's health, science and environment editor.
Allyson Chiu is a reporter focusing on wellness for The Washington Post. She previously worked overnight on The Post's Morning Mix team.