Health
a health care provider prepares a vaccine for a mature woman
a health care provider prepares a vaccine for a mature woman
a health care provider prepares a vaccine for a mature woman

Booster Shots, Third Doses and Additional Doses for COVID-19 Vaccines: What You Need to Know

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COVID-19 vaccine boosters and additional vaccine doses are now authorized by the U.S. Food and Drug Administration (FDA) and recommended by the U.S. Centers for Disease Control and Prevention (CDC) for certain people.

Lisa Maragakis, M.D., M.P.H., senior director of infection prevention, and Gabor Kelen, M.D., director of the Johns Hopkins Office of Critical Event Preparedness and Response, explain what you need to know about these COVID shots.

What is a COVID-19 vaccine booster?

A COVID booster shot is an additional dose of a vaccine given after the protection provided by the original shot(s) has begun to decrease over time. Typically, you would get a booster after the immunity from the initial dose(s) naturally starts to wane. The booster is designed to help people maintain their level of immunity for longer.

Who can get a COVID-19 vaccine booster?

The CDC recommends a COVID-19 booster if you are 18 or older and:

  • Received the Janssen/Johnson & Johnson vaccine at least two months ago.
  • Received both shots of either the Moderna or Pfizer COVID-19 vaccine at least six months ago. 

Individuals who have a medical condition associated with immunosuppression are eligible to receive an additional vaccine dose.

Please visit the CDC website for the latest information on vaccine boosters.

What are COVID booster side effects?

After getting vaccinated for COVID-19, you might experience some temporary symptoms similar to those you might notice when you get a flu shot, such as a sore, swollen arm where you got the shot. You might run a fever and experience body aches, headaches and tiredness for a day or two. Chills, swollen lymph nodes can also occur.

These symptoms do not mean you are sick. They signal that your immune system is responding to the shots and building up protection against the coronavirus.

Where can I get a COVID vaccine booster?

Please check your state or local resources. Retail pharmacies, mobile vaccination clinics (walk-up) and state and local vaccination sites offer booster appointments. Some locations may offer walk-up vaccination times.

Johns Hopkins Medicine has limited booster/additional dose appointments at some of its Maryland locations.

What is an additional dose of the coronavirus vaccine?

An additional dose, originally called a third dose, is given to people with moderately or severely compromised immune systems to improve their response to the initial vaccine series. (The term “third dose” was used to refer to additional doses for the two mRNA vaccines, but now the term is “additional dose” because those who received a J&J “one dose” may also be eligible for a dose based on their immune systems.)

What is the difference between a booster and an additional dose?

A COVID-19 booster is given when a person has completed their vaccine series, and protection against the virus has decreased over time. Depending on the original series you had, some details will vary. Please review the booster eligibility information above and talk to your health care provider if you are not sure if you meet these guidelines. Please note, if you receive the Moderna booster, you will receive half of the original Moderna dose.

An additional dose is administered to people with moderately to severely compromised immune systems. This additional dose is intended to improve immunocompromised people’s response to their initial vaccine series. Depending on the original series given, some details will vary. Please review the additional dose eligibility information and talk to your health care provider if you are not sure if you meet these guidelines.

Who can get an additional dose of a COVID-19 vaccine?

The CDC and the FDA recommend an additional dose if you:

  • Have been receiving active cancer treatment for tumors or cancers of the blood
  • Received an organ transplant and are taking medicine to suppress the immune system
  • Received a stem cell transplant within the last two years, or are taking medicine to suppress the immune system
  • Are diagnosed with moderate or severe primary immunodeficiency (such as DiGeorge syndrome or Wiskott-Aldrich syndrome)
  • Are diagnosed with HIV and have a high viral load or low CD4 count, or are not currently taking medication to treat HIV
  • Are taking drugs like high-dose steroids or other medications that may cause severe suppression of the immune system

If you are not sure whether you fit into any of these categories, please contact your medical provider. For more details, please review the CDC’s information for moderately to severely immunocompromised people.

When should I get an additional dose of COVID vaccine?

If you are immunosuppressed and originally received the Moderna or Pfizer COVID-19 vaccine, you can get an additional dose when it has been at least 28 days since your second shot.

If you got the Janssen/Johnson & Johnson COVID-19 vaccine, you can get an additional dose when it has been at least 2 months since your vaccine.

Does my COVID booster or additional dose have to be the same brand that I got before?

No, you can mix and match brands. The FDA has authorized three vaccine boosters — Pfizer-BioNTech, Moderna and Janssen/Johnson & Johnson — and determined that it is safe to get a COVID-19 vaccine booster or additional dose that is a different brand than your initial dose or doses. If you get the Moderna booster, you will receive half of the original Moderna dose. Please be sure to confirm this with the person giving you this shot.

syringe close up - covid19 coronavirus vaccine

COVID-19 Vaccine

Get information and updates from Johns Hopkins Medicine.

Updated on November 22, 2021