More than 100 million Americans have been vaccinated against COVID-19. The United States hopefully is headed toward stopping the spread of the disease. But researchers don’t know how long immunity from the currently authorized vaccines lasts.

Public health experts also are carefully watching COVID-19 variants to see whether the vaccines protect against them. Some public health experts are looking at whether people will need booster shots against COVID-19.

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What Is a Booster Shot?

Public health officials and vaccine producers are discussing two possible extra shots. The first is a regular booster shot — that is, another dose of the same vaccine you already received. The goal of this shot is to “boost” your immune response.

This type of booster shot isn’t usually different than the original vaccine. Instead, it ensures your immune system is ready to respond if you are exposed to the virus.

The other type of booster shot is one that trains your immune system to recognize different COVID-19 variants. These are versions of the SARS-CoV-2 virus that have a mutations, or significant differences in genetic code. These mutations might help the virus get past the immune system of a vaccinated person.

Right now, the Pfizer/BioNTech, Moderna, and J&J vaccines are effective in preventing severe disease and death from the variants spreading widely in this country. But they are less effective at preventing mild illness from some of these variants. These include the variants from South Africa, Brazil, and California.

Will There Be a COVID-19 Booster Shot?

It’s very likely that each company will produce a regular booster shot, an updated booster shot against one variant, or both. Pfizer announced it has begun testing booster shots and vaccines against the variants.

The CEOs of Moderna and J&J also expect booster shots to become necessary for their vaccines. Moderna has already sent regular booster shots and updated shots against the variants to the National Institutes of Health for further study. J&J also has begun testing a second dose of its one-dose vaccine and an updated vaccine against variants.

Why Would a Booster Shot Be Necessary?

People may need booster shots if the antibodies built up after vaccination start to decrease over time. That’s why some vaccines, such as the tetanus shot, require boosters after a certain number of years.

Although all three companies have begun testing or making booster shots, it’s still not certain that boosters will be necessary. It depends on how long protection from the current vaccines lasts or whether variants cause more COVID-19 cases in vaccinated people. Scientists won’t know how long protection lasts until enough time passes after people have been vaccinated.

Anthony Fauci, MD, director of the National Institute of Allergy and Infectious Disease, said that current vaccines last at least 6 months. He expects they could last for a year as well.

Researchers will know protection is wearing off if more “breakthrough” cases start occurring. A breakthrough case is a COVID-19 infection in someone who was fully vaccinated against the virus.

As of April 26, the Centers for Disease Control and Prevention has received reports of 9,245 breakthrough cases. But that’s out of 95 million total people vaccinated in the U.S. As more people receive the vaccine and more time passes, the number of breakthrough cases will rise.

If the speed of breakthrough infections also rises, that may mean protection from the vaccines has started to wear off. Also, if a new variant causes more infections in vaccinated people, we might need a booster for that variant.

When boosters become necessary also depends on when there’s data showing the current vaccines are less effective.

For more information on UPMC’s efforts against COVID-19, visit


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About UPMC

Headquartered in Pittsburgh, UPMC is a world-renowned health care provider and insurer. We operate 40 hospitals and 700 doctors’ offices and outpatient centers, with locations in central and western Pennsylvania, Maryland, New York, and internationally. We employ 4,900 physicians, and we are leaders in clinical care, groundbreaking research, and treatment breakthroughs. U.S. News & World Report consistently ranks UPMC Presbyterian Shadyside as one of the nation’s best hospitals in many specialties and ranks UPMC Children’s Hospital of Pittsburgh on its Honor Roll of America’s Best Children’s Hospitals.