What Is the Covid-19 Vaccine Booster?

Reviewed on 10/25/2021

Of the three COVID-19 vaccines authorized for use in the U.S. that have been shown to be highly effective in reducing the risk of severe disease (including the Delta variant), hospitalization, and death, two of them require boosters. The Modern and Pfizer COVID-19 vaccines involve two shots, while the Johnson & Johnson vaccine involves just one shot.
Of the three COVID-19 vaccines authorized for use in the U.S. that have been shown to be highly effective in reducing the risk of severe disease (including the Delta variant), hospitalization, and death, two of them require boosters. The Modern and Pfizer COVID-19 vaccines involve two shots, while the Johnson & Johnson vaccine involves just one shot.

The Centers for Disease Control (CDC) recommends all eligible individuals be vaccinated against the virus that causes COVID-19. The U.S. Food and Drug Administration (FDA) has issued emergency use authorizations (EUAs) for COVID-19 vaccines to allow for the use of a single booster dose as well.

What Vaccines Are Available for COVID-19 and Which Ones Require Boosters? 

The FDA has approved one vaccine for the prevention of COVID-19

  • Pfizer-BioNTech COVID-19 vaccine 
  • May be given to individuals 16 years and older
  • Emergency use authorization (EUA) for individuals 12 years and older
  • Requires 2 shots administered 3 weeks apart

Two additional vaccines have emergency use authorizations (EUAs) for use to prevent coronavirus disease 2019 (COVID-19) caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2): 

  • Moderna COVID-19 vaccine 
    • May be given to individuals 18 years and older
    • Requires 2 shots administered 4 weeks apart
  • Johnson & Johnson (Janssen)
    • May be given to individuals 18 years and older
    • Requires just one injection 

Which COVID-19 Vaccines Are Effective?

All three of the COVID-19 vaccines authorized for use in the U.S. have been shown to be highly effective in reducing the risk of severe disease, hospitalization, and death, even against the highly contagious Delta variant. 

  • However, antibodies produced from the vaccines that help protect against COVID-19 wear off over time. A COVID-19 vaccine booster helps extend the protection for a longer period. 
  • Emergency use authorizations (EUAs) for COVID-19 vaccines allow for the use of a single booster dose. 

Who Should Get a COVID-19 Vaccine?

Certain groups of people who received a Pfizer-BioNTech or Moderna COVID-19 vaccine are eligible for a booster shot at 6 months or more after their initial series:

  • 65 years and older
  • Age 18 years and older who live in long-term care settings
  • Age 18 years and older who have underlying medical conditions
  • Age 18 years and older who work in high-risk settings
  • Age 18 years and older who live in high-risk settings

For people who got the Johnson & Johnson COVID-19 vaccine, booster shots are also recommended for individuals 18 years and older and who were vaccinated two or more months ago.

Each of the available COVID-19 vaccines may be used as a “mix and match” booster dose in eligible individuals following completion of primary vaccination with a different available COVID-19 vaccine.

How Do COVID-19 Vaccines and Boosters Work?

Vaccines help the body produce immunity to infection by imitating the infecting agent. Vaccines almost never cause serious illness, but instead boost the body’s adaptive immune function to produce T-lymphocytes and antibodies (parts of the immune system that help the body fight germs).

  • Once the simulated infection created by the vaccine goes away, the body has a “memory” of T-lymphocytes and B-lymphocytes that remember how to fight that infection in the future.
  • Following immunization, it can take several weeks for the body to produce the produce T-lymphocytes and B-lymphocytes needed to fight infection, so it is possible a person could become infected with COVID just before or just after vaccination because the body has not yet had time to build its defenses. 
  • The first set of vaccinations helps train the body’s immune system to recognize the virus and fight off the infection. The booster shot helps strengthen or prolong that immune response. 

What Are the Side Effects of the COVID-19 Vaccines and Boosters?

After the COVID-19 vaccine is administered and the body is building its defenses, people may experience mild side effects starting a day or two after receiving the vaccine that can last a few days. This is normal and expected and a sign the body’s immune system is responding as it should. 

People may also experience similar side effects when receiving the COVID-19 vaccines booster shot. 

Common side effects and reactions to the COVID-19 vaccines and boosters include:

What Are the Serious Side Effects?

Rarely, severe allergic reactions, including anaphylaxis, can occur after receiving any vaccine.

  • This type of reaction has only occurred in about 2 to 5 people per million vaccinated in the U.S. These kinds of allergic reactions usually occur within 30 minutes after vaccination and can be immediately and effectively treated.
  • People who are allergic to specific ingredients in the current vaccines are advised to avoid that particular vaccine. Those prone to allergic reactions, but who do not have a known allergy to a component of the vaccine, are advised to receive the vaccine in a healthcare facility and to wait 30 minutes (instead of 15) following an injection. 

There is a Vaccine Adverse Event Reporting System (VAERS) in place for patients to report unexpected vaccine side effects.

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Reviewed on 10/25/2021
References
https://www.cdc.gov/coronavirus/2019-ncov/vaccines/different-vaccines.html

https://www.cdc.gov/media/releases/2021/p1021-covid-booster.html

https://www.cedars-sinai.org/blog/understanding-vaccine-boosters.html

https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-takes-additional-actions-use-booster-dose-covid-19-vaccines