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What to Know About the Coronavirus Vaccines

Questions continue as millions of Americans get immunized

image of a vial labeled coronavirus vaccine

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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.

One vaccine (from Pfizer-BioNTech) has received full approval from the U.S. Food and Drug Administration (FDA) and two others (one from Moderna and another from Johnson & Johnson) are being administered under 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.

The EUA process is faster than standard FDA approval, which can take six to 10 months. However, data proving safety and effectiveness is still required for authorization, and the FDA and an advisory committee of experts use this data to weigh the risks and benefits of the product in question.

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 if he ever comes across the real germ.

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 when it encounters the real thing in the future,” says Tony Moody, associate professor of pediatrics and immunology at 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.”

In the case of the new coronavirus, a vaccine makes a person resistant to an infection from the virus and the illness it causes — COVID-19 — or, at least, enables a person who becomes infected to have “a shorter course [of disease] or not as many complications,” Moody adds.

What coronavirus vaccines are available now?

The vaccines from Pfizer-BioNTech, Moderna and Johnson & Johnson (J&J) are so far the only products available to Americans.

Pfizer’s vaccine is approved for people 16 and older and is available for people ages 12-15 under emergency use authorization; Moderna and J&J's vaccines have been authorized for people 18 and older.

The three vaccines have been found to be highly effective at preventing COVID-19 in clinical trial participants and in real-world data. A large study looking at a diverse population of fully vaccinated health care workers found the two-dose mRNA vaccines from Pfizer-BioNTech and Moderna reduced the risk of getting sick with COVID-19 by 94 percent. In a separate study, researchers found the Pfizer-BioNTech and Moderna vaccines were 94 percent effective against COVID-19 hospitalization among fully vaccinated adults 65 years and older.

J&J’s product has been found to be 66 percent effective overall and 72 percent effective in U.S.-based clinical trials.

Are the vaccines safe?

Safety is a key concern among health officials and experts. Participants in the Pfizer-BioNTech, Moderna and Johnson & Johnson trials experienced side effects after vaccination, including injection-site pain, fever, chills, headaches, muscle aches and joint pain. These symptoms are temporary and are in line with side effects some people experience from other vaccines, including the flu shot and the vaccine to prevent shingles.

More serious reactions are rarer, but they do occur. On April 13, the CDC and FDA recommended that U.S. vaccination sites pause their use of the Johnson & Johnson vaccine while the agencies review data involving six reported cases of a rare but serious type of blood clot, called cerebral venous sinus thrombosis, in individuals after they received the vaccine. One case was fatal and one patient was in critical condition.

All six cases occurred in women between the ages of 18 and 48, six to 13 days after vaccination. People who recently received the Johnson & Johnson vaccine and develop symptoms of severe headache, abdominal pain, leg pain or shortness of breath within three weeks after vaccination should contact their health care provider, officials say.

Also, providers should be on the lookout for patients who present with these symptoms and be advised that “treatment of this specific type of blood clot is different from the treatment that might typically be administered,” according to a joint statement from the CDC and FDA. “Usually, an anticoagulant drug called heparin is used to treat blood clots. In this setting, administration of heparin may be dangerous, and alternative treatments need to be given.”

On April 23, CDC’s Advisory Committee on Immunization Practices (ACIP) recommended to the CDC director that the pause be lifted. A notice to women age 50 and under would be added to the fact sheets the government provides to people getting vaccinated.

To date, no cases of cerebral venous sinus thrombosis have been linked to the Moderna and Pfizer-BioNTech vaccines. However, a small number of allergic reactions, including anaphylaxis, have been reported, according to early safety monitoring data from the CDC. Though an anaphylactic reaction is potentially life-threatening, it can be quickly halted as it was in these six cases, with medicines such as epinephrine. Because of this, the CDC is recommending that anyone who has ever had a severe allergic reaction to any ingredient in a COVID-19 vaccine abstain from receiving it. If you have a history of severe allergic reactions to other vaccines, ask your doctor if you should get a COVID-19 vaccine, the agency advises.

Another rare but possible side effect linked to the J&J vaccine: Guillain-Barré syndrome, a neurological disorder in which the immune system attacks and damages nerve cells. In most of the cases the syndrome occurred within 42 days of someone getting the J&J vaccine. The FDA has not modified its EUA for the J&J vaccine and says the chances of this syndrome emerging are “very low.”

Mild cases of inflammation of the heart muscle and surrounding tissue (called myocarditis and pericarditis) have also been reported among younger people following COVID-19 vaccination. Health officials determined this is an “extremely rare side effect” and are still encouraging anyone eligible for a vaccine to get one.

After a vaccine is authorized, many vaccine safety monitoring systems watch for adverse events. If one is discovered, “experts quickly study it further to assess whether it is a true safety concern” and then adjust vaccine recommendations as needed, the CDC explains. Safety monitoring also continues after vaccine approval.

How much does the vaccine cost?

The federal government pre-purchased hundreds of millions of vaccine doses with taxpayer money, and Americans will not have to pay to receive them.

Vaccine providers are able to charge an administration fee for giving the shot, but this fee should be covered by public or private insurance, or by a government relief fund for the uninsured.

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

Cases of infection post-vaccine, called breakthrough cases, are being reported, but experts stress they are still relatively uncommon. What’s more, it’s rare to get an infection that results in hospitalization or death once you are fully vaccinated. 

According to data collected by the CDC, less than 1 percent of fully vaccinated Americans have been hospitalized or have died from COVID-19. The vast majority of serious illness and death is occurring in unvaccinated individuals. 

Breakthrough infections, however, can contribute to the spread of COVID-19. New data show that fully vaccinated people who become infected with the delta variant can pass the virus on to others, which is why health officials now recommend that vaccinated individuals in areas of high community transmission wear a face mask in indoor public settings. 

“The masking recommendation was updated to ensure the vaccinated public would not unknowingly transmit virus to others, including their unvaccinated or immunocompromised loved ones,” CDC Director Rochelle Walensky said. 

Are both doses really necessary?

Both the Pfizer-BioNTech and Moderna vaccines require two doses and following through with both doses is necessary to ensure effectiveness. The J&J vaccine only requires one dose.

According to the CDC, the first shot starts building protection, while the second shot “is needed to get the most protection the vaccine has to offer.” Getting the full-dose regimen is also key to mounting protection against the coronavirus variants of concern, including the highly contagious delta variant. Studies show one dose is much less effective at fighting off the virus, compared to the complete series.

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

Even if you had COVID-19, the CDC still recommends getting vaccinated. “That’s because experts do not yet know how long you are protected from getting sick again after recovering from COVID-19. Even if you have already recovered from COVID-19, it is possible — although rare — that you could be infected with the virus that causes COVID-19 again,” the agency explains.

Have questions? Talk to your doctor.

“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.”


Tony Moody, M.D., associate professor of pediatrics and immunology at Duke University School of Medicine and a principal investigator at the Duke Human Vaccine Institute

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, M.D., 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.

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