COVID-19 BOOSTER SHOTS: WHAT YOU NEED TO KNOW

Update: As of December 9, 2021, the FDA has granted emergency authorization for Pfizer/BioNTech’s COVID-19 vaccine booster to everyone 16 and older.


On October 20, 2021, the US Food and Drug Administration (FDA) updated the emergency use authorizations for COVID-19 vaccines to allow for the use of a single booster dose for those in eligible populations. On November 19, 2021, the FDA expanded eligibility for booster doses, and now all people 18 years and older are eligible for a booster shot depending on the timing of their last dose of their primary series. On November 29, 2021, the CDC has strongly encouraged for people over 18 to receive a booster shot depending on the timing of the last dose of their primary series, as follows: 

  • mRNA vaccines (Moderna ): The single dose booster for the Moderna COVID-19 Vaccine and the Pfizer BioNTech COVID-19 Vaccine may be administered at least 6 months after completion of the primary series.
  • mRNA vaccines (Pfizer): The single dose booster for the Pfizer BioNTech COVID-19 Vaccine may be administered to people 16 years and older if they are at least 6 months post their initial Pfizer vaccination series
  • Adenovirus vector vaccine (Johnson and Johnson): The use of a single booster dose of the Janssen (Johnson and Johnson) COVID-19 Vaccine may be administered at least 2 months after completion of the single-dose primary regimen. The CDC recommends all people 18 years and older should receive a booster shot at least 2 months after receiving their Johnson & Johnson/Janssen COVID-19 vaccine.

The mix and match approach – what’s allowed?

The FDA has also authorized the “mix and match” approach for booster doses, meaning a single booster dose of any authorized COVID-19 vaccine can be administered to eligible persons regardless of the vaccine series originally completed. This authorization follows extensive research on the efficacy and safety of this approach against other diseases as well as COVID-19.  Most recently, a study from the National Institute of Allergy and Infectious Diseases found the known and potential benefits of using a single “mix and match” COVID-19 booster dose outweighs the known and potential risks of their use. 

All of the COVID-19 vaccines currently available in the US – Pfizer, Moderna, and Johnson and Johnson – have a version of a booster shot available. 

If it has been 6 months since an individual who is 18 years or older has completed their primary mRNA vaccine (Pfizer or Moderna) series, they can take any of the available booster shots. 

If it has been 2 months since a person who is 18 years or older has received the Johnson and Johnson vaccine, they can take any of the available booster shots. 

Don’t know which booster shot to get? 

The authorized “mix and match” strategy not only allows for convenience and accessibility for those who should receive a booster shot, it is also rooted in the science of safety and efficacy for doing so. 

Deciding which booster dose to take depends on your personal health which should be discussed with your healthcare provider and your comfortability with receiving the one available at the time, or the familiarity you have with the series you received originally. 

Booster versus an additional dose 

If you have a moderately to severely compromised immune system, the Centers for Disease Control and Prevention (CDC) recommends an additional dose of an mRNA COVID-19 vaccine at least 28 days after your second Pfizer-BioNTech or Moderna vaccine shot. Data suggests that persons with moderately to severely compromised immune systems do not build the same immunity against COVID-19 compared to persons who are not immunocompromised.

An additional COVID-19 vaccine dose is different than a booster shot: 

  • An additional dose is for those whose immune system response to the initial vaccine series (1-2 shots, depending on the specific vaccine you received) isn’t sufficient to protect against the virus (usually persons who are immunocompromised).
  • booster shot is for persons whose immune response to a vaccine diminishes due to time, which is referred to as waning immunity. 

To learn more about COVID-19 vaccines and treatments, check out our COVID-19 Vaccines page and COVID-19 Therapeutics page.