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What to Know About the Coronavirus Vaccines

Questions continue as millions of Americans get immunized and boosted

Photograph of a medical vial labeled coronavirus vaccine, injection only, 5 ml
Manjurul/Getty Images

Latest updates

Bivalent boosters are effective against latest circulating variants. The newly updated COVID-19 boosters formulated to target the BA.4 and BA.5 omicron subvariants that were circulating in the summer and fall are effective at preventing mild illness caused by some of the newer variants, including XBB.1.5, which is now the dominant strain in the U.S. A new report from the Centers for Disease Control and Prevention (CDC) found that these so-called bivalent boosters cut the risk of a symptomatic infection nearly in half in adults ages 18 to 49. The boosters were 40 percent effective against symptoms from a coronavirus infection among individuals 50 to 64 years old, and 43 percent effective among those 65 and older. So far, about 15 percent of the U.S. population has received this updated booster. Coverage is highest (nearly 40 percent) among adults 65 and older, the latest CDC data shows.

Health officials continue to recommend bivalent boosters for older adults. The CDC and Food and Drug Administration issued a joint statement on Jan. 13 to inform the public that no changes are being made to vaccine recommendations after one safety monitoring system detected a possible increased risk for stroke in adults 65 and older who received a bivalent shot from Pfizer-BioNTech. The issue was flagged by a real-time surveillance system; no other safety systems or databases have shown a similar signal, the agencies said. “Although the totality of the data currently suggests that it is very unlikely that the signal in VSD [Vaccine Safety Datalink] represents a true clinical risk, we believe it is important to share this information with the public, as we have in the past, when one of our safety monitoring systems detects a signal,” the statement said. Health officials say they will "continue to evaluate additional data from these and other vaccine safety systems" and that more information will be discussed at the upcoming Vaccines and Related Biological Products Advisory Committee meeting on Jan. 26. In the meantime, "staying up-to-date with vaccines is the most effective tool we have for reducing death, hospitalization and severe disease from COVID-19," the CDC and FDA said. Data shows that an updated bivalent vaccine reduces the risk of hospitalization from COVID-19 by nearly threefold compared to those who were previously vaccinated but have not yet received the updated vaccine.

Updated boosters cut risk of hospitalization, new research shows.study published by the CDC on Dec. 16 found that adults 65 and older who received an updated bivalent COVID-19 booster saw their risk of hospitalization reduced by 73 percent compared with peers who received the original COVID-19 vaccines only. Another study, also published by the CDC on Dec. 16, found that the new omicron-targeting boosters may reduce the risk of severe COVID-19 in all adults by 50 percent or more. Health officials encourage all people eligible for a bivalent booster to get one as soon as possible, in an effort to avoid a winter surge of severe illness. “With co-circulation of multiple respiratory viruses, including SARS-CoV-2 (COVID), influenza, and respiratory syncytial virus (RSV), vaccination against respiratory diseases for which vaccines are available is especially important to prevent illnesses resulting in health care encounters and to reduce strain on the health care system,” the authors of one of the CDC reports wrote

Bivalent vaccines are now available for kids as young as 6 months. Children 6 months through 5 years old who are fully vaccinated with Moderna’s COVID-19 vaccine are eligible to receive an updated bivalent booster shot, the CDC said Dec. 9. Kids 6 months through 4 years old who were vaccinated with Pfizer and have not received their third dose in the primary series can receive a bivalent vaccine for their third shot, though this is not considered a booster. The bivalent vaccines target some of the more recently circulating strains of the coronavirus. These shots have been available to adults since September. About 42 million Americans have rolled up their sleeves for the new booster, which public health experts say is critical to combating a wave of severe illness this winter.

CDC authorizes Novavax booster for adults. CDC Director Rochelle Walensky approved the Novavax COVID-19 booster for adults 18 and older. In her decision memo, Walensky gives adults the option “to receive a Novavax monovalent booster instead of an updated (bivalent) Pfizer-BioNTech or Moderna booster if they have completed primary series vaccination but have not previously received a COVID-19 booster — and if they cannot or will not receive mRNA vaccines.” The authorization came on the heels of Novavax’s two-shot COVID-19 vaccine series being approved for ages 12 to 17, as well as for adults 18 and older. The two doses of the Novavax vaccine are given three weeks apart. Novavax’s product uses a different, more traditional technology than the other COVID-19 vaccines on the market. Instead of prompting the body to make its own version of the spike protein (a key part of the virus), the protein is made in a lab and delivered directly upon injection. “If you have been waiting for a COVID-19 vaccine built on a different technology than those previously available, now is the time to join the millions of Americans who have been vaccinated,” Walensky said when the vaccine was first authorized for adults in July. “With COVID-19 cases on the rise again across parts of the country, vaccination is critical to help protect against the complications of severe COVID-19 disease."

Researchers around the world have been working at record speed to develop vaccines to combat COVID-19. Less than a year after the start of the pandemic, that goal became a reality.

Two vaccines (from Pfizer-BioNTech and Moderna) have received full approval from the U.S. Food and Drug Administration (FDA), and two others (from Johnson & Johnson and Novavax) are being administered under a limited emergency use authorization (EUA). This FDA designation allows access to treatments and other medical tools during a public health emergency when no other options exist.

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What, exactly, is a vaccine?

A vaccine is something that helps a person build up immunity to an infectious disease. It works by intentionally introducing the body to an inactive form of a disease-causing germ, or something similar to it. This then stimulates the immune system’s production of antibodies, the proteins that help to protect the person from a future infection.

Think of it like a workout for your immune system: You’re “sending it to the gym and preparing it to be able to do something” in case it meets up with the germ, explains Tony Moody, associate professor of pediatrics and immunology at the Duke University School of Medicine and a principal investigator at the Duke Human Vaccine Institute. “Essentially, what a vaccine is doing is teaching the immune system how to handle something before you actually encounter the real thing — so that, hopefully, when you do encounter the real thing, you’re able to deal with it quickly and get rid of it,” he says.

What coronavirus vaccines are available now?

The vaccines from Pfizer-BioNTech, Moderna, Johnson & Johnson (J&J) and Novavax are the only products available to Americans. The CDC recommends the Pfizer and Moderna vaccines over the J&J vaccine single-shot version because a rare but serious blood-clotting disorder has been linked to it. But J&J’s vaccine is still available for people who are “unable or unwilling to receive an mRNA vaccine,” the CDC says.

Pfizer’s vaccine is approved for people 16 and older but is available for people ages 6 months through 15 years under emergency use authorization. Moderna’s vaccine is also authorized for kids 6 months and up and is approved for people 18 and older. The vaccine from Novavax is authorized for people 12 and up, and J&J’s shot is authorized for adults 18 and older.

The four vaccines lower your risk of getting infected with the virus and have been found to be highly effective at preventing severe illness from an infection. Hospitalizations in September 2022 were 4.5 times higher in unvaccinated individuals age 65 and older, compared to their vaccinated and boosted peers, federal data shows. Updated booster shots from Pfizer and Moderna are also available and recommended for children 5 and older and for some children as young as 6 months old. These new vaccines (known as bivalent boosters) target the original strain of the coronavirus and also more recently circulating versions of the virus to provide a broader swath of protection. 

Are the vaccines safe?

Participants in the clinical trials testing the vaccines experienced side effects, including injection-site pain, fever, chills, headaches, muscle aches and joint pain. These symptoms are usually mild to moderate in severity and are temporary. They are also in line with side effects that some people experience from other vaccines, including the flu shot and the vaccine to prevent shingles.

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More serious reactions have occurred but are rare. Anaphylaxis, a severe allergic reaction, has happened in a small number of people after COVID vaccination, the CDC says. This is why you may be asked to wait about 15 minutes after your shot or booster to monitor for symptoms. Vaccine providers are equipped with medicines to quickly treat the reaction.

Health officials are also monitoring rare reports of myocarditis and pericarditis in adolescents and younger adults who have received the Pfizer,Moderna and Novavax vaccines. Most of these patients who received care responded well to medicine and felt better quickly, the CDC says.

Another uncommon event that has been linked to J&J’s vaccine is a rare but serious clotting disorder, called thrombosis with thrombocytopenia syndrome. Sixty cases of the condition were confirmed as of March 2022; nine were fatal. Young women in their 30s and 40s are most at risk. After reviewing evidence of the adverse event, the CDC decided in December 2021 to recommend Pfizer’s and Moderna’s vaccines over J&J’s version; months later, the FDA limited its use. J&J’s vaccine, however, is still available to those who are “unable or unwilling” to get the Pfizer or Moderna vaccine.

How much does the vaccine cost?

The federal government purchased hundreds of millions of vaccine doses with taxpayer money, so Americans do not have to pay to receive them, including the booster shots, though this could change in the future.

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Can I still get COVID-19 after getting the vaccine?

Because no vaccine is 100 percent effective, breakthrough infections can occur, and more are being reported as omicron and its subvariants rip through the country. But experts stress that the vaccines and boosters remain highly protective against hospitalization and death.

Breakthrough infections, however, can contribute to the spread of COVID-19, which is why health officials recommend that vaccinated individuals in areas of high community transmission wear a face mask in indoor public settings.

Do I need the vaccine if I have already had COVID-19?

Even if you had COVID-19, the CDC recommends getting vaccinated and boosted, since research has not yet shown how long protection from a previous coronavirus infection lasts. Plus, the vaccine may afford better protection against COVID-19 than a previous infection. Unvaccinated people who already had COVID-19 had greater odds of getting COVID-19 again, compared to fully vaccinated people, a CDC study found.

Have questions? Talk to your doctor.

Is it good to have more than one vaccine available?

Absolutely. “In fact, it’s highly desirable,” says William Schaffner, an infectious disease expert and professor at Vanderbilt University School of Medicine, because that would mean “there would be more vaccine manufacturers working to actually produce the vaccine, and so we could more expeditiously try to vaccinate the population in the United States and beyond.”

Kathleen Neuzil, professor in vaccinology and director of the Center for Vaccine Development and Global Health at the University of Maryland School of Medicine, echoes Schaffner’s sentiment and points to the flu vaccine for comparison: There are multiple formulations on the market, including the injectable high-dose vaccine and the nasal spray vaccine, for example, which are recommended for different populations.​

“We really need every person on Earth, theoretically, to be able to receive this vaccine. So, to me, [having more than one option] is a positive, because we need so much,” she adds.​

Editor’s note: This article, originally published May 1, 2020, has been updated to reflect new information.