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

Featured Experts:

Updated on January 28, 2022

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 most people, as soon as they are eligible.

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. The booster helps people maintain strong protection from severe coronavirus disease.

Why do I need a booster, since the COVID-19 vaccines are effective?

The protection offered by the FDA-approved and authorized vaccines is very powerful, but it starts to weaken after two months for the Johnson & Johnson vaccine, and after five months for the Pfizer and Moderna vaccines. Getting a booster shot extends the protection, even against the delta and omicron variants.

Two studies released by the CDC (one conducted April–December 2021 and the other from August 2021–January 2022) show that being fully vaccinated (getting both doses of the Pfizer or Moderna vaccine or one Johnson & Johnson vaccine) plus receiving a booster provides greater protection from severe disease, hospitalization and death due to COVID-19 compared to only being fully vaccinated. A third study, published in the Journal of the American Medical Association, shows similar results. The research also indicates that the booster offers greater protection against the delta and omicron variants than being fully vaccinated or not vaccinated at all.

The CDC recommends that people who are vaccinated get a booster dose when they are eligible, and that they stay up to date with COVID-19 vaccinations.

Who can get a COVID-19 vaccine booster?

The CDC recommends a COVID-19 booster if you are:

  • Age 18 or older and you received the Janssen-Johnson & Johnson vaccine at least two months ago
  • Age 18 or older and you received both required doses of the Moderna vaccine at least five months ago (your booster will be a one-half dose)
  • Age 12 or older and you received both required doses of the Pfizer-BioNTech vaccine at least five months ago (the Pfizer-BioNTech vaccine is the only vaccine and booster authorized for children and teens ages 12–17)
  • The CDC recommends that you get vaccinated and boosted even if you previously had COVID-19 infection. Before getting a shot, be sure you have followed isolation and quarantine guidelines so you do not infect others, and discuss your COVID-19 history with the medical team.

Can children get a COVID-19 booster?

Yes, the CDC recommends that children and teens age 12 and older receive a booster when eligible. Since the Pfizer vaccine is currently the only authorized vaccine for those under age 18, children 12 and older should receive a booster five months after their second Pfizer shot.

Children age 5 and older who have certain medical conditions associated with immunosuppression can receive an additional dose 28 days after their second 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-19 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.

Should I get an additional COVID-19 vaccine dose if I have a weakened immune system?

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

This additional dose is given to people with moderately or severely compromised immune systems to improve their response to the initial vaccine series.

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 when eligible for those who are immunocompromised and ages 5 and older. This includes those who:

  • 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

The CDC also recommends a booster shot three months after the additional primary shot for those who received the Pfizer or Moderna vaccine, and two months after the one-shot Johnson & Johnson vaccine.

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-19 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 two months since your vaccine.

Does my COVID-19 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. 

The Pfizer-BioNTech vaccine and booster are the only ones authorized for children and teens ages 12–17.

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 the shot.

syringe close up - covid19 coronavirus vaccine

COVID-19 Vaccine

Get information and updates from Johns Hopkins Medicine.