Third Dose/Booster Shot FAQ

Additional Dose and Booster Shot FAQ

Is an additional dose the same as a booster shot?

No. An additional dose is different from a booster dose.

Some people, those who are immunocompromised, may not develop the same immune response level after vaccination as others. An additional dose is recommended for those individual to help them build the same level of immunity as people who are not immunocompromised.

A booster shot is recommended as protection from the vaccine wanes over time.

Who should get a booster shot of COVID-19 vaccine?

On Thursday, December 9, 2021, the Centers for Disease Control and Prevention recommended everyone 16 years and older receive a booster shot. At this time, only the Pfizer-BioNTech COVID-19 vaccine is authorized and recommended for those aged 16 and 17 years.

On Friday, November 19, 2021, the U.S. Food and Drug Administration amended the emergency use authorizations (EUA) for both the Moderna and Pfizer-BioNTech COVID-19 vaccines authorizing use of a single booster dose for all individuals 18 years of age and older after completion of primary vaccination with any FDA-authorized or approved COVID-19 vaccine.

For Moderna and Pfizer-BioNTech COVID-19 vaccines, a single COVID-19 vaccine booster dose is recommended 5 months after completion of an mRNA primary series. The Moderna booster dose is a smaller 50 microgram dose.

For Janssen (Johnson & Johnson) COVID-19 vaccine, a single COVID-19 vaccine booster dose is recommended for people aged 18 years and older, 2 months after receipt of the initial Johnson & Johnson dose, under the FDA’s Emergency Use Authorization.

Who should get an additional dose of vaccine?

Currently, individuals with moderately to severely compromised immune systems are recommended for an additional dose of COVID-19 vaccine if they previously received a two-dose primary series of either the Pfizer BioNTech or Moderna COVID-19 vaccines.   This includes people currently receiving treatment for cancer, people taking medications that weaken the immune systems, organ or stem cell transplant recipients, individuals with advanced or untreated HIV infection, and other conditions.  A full list of conditions can be found on CDC’s website.  If you are unsure if you are recommended for an additional dose, talk with your health care provider.  The third dose of Pfizer BioNTech or Moderna COVID-19 vaccine can be given anytime 28 days after receiving the second dose.

An additional dose is being recommended after emerging data suggests some people with moderately to severely compromised immunes systems do not always build the same level of immunity as individuals who do not have a compromised immune system.  An additional dose will help ensure people with compromised immune systems get as much protection as possible from COVID-19 vaccination.

More information can be found here: COVID-19 Vaccines for Moderately to Severely Immunocompromised People | CDC

Can I get any type of COVID-19 vaccine for the additional dose or booster dose?

The CDC stated that the use of each of the available COVID-19 vaccines as a heterologous (or “mix and match”) booster dose in eligible individuals, following completion of primary vaccination with a different available COVID-19 vaccine, is allowable. Allowing mixing and matching could alleviate supply issues, make the task of getting a booster simpler for Americans and allow people who may have had adverse reactions to the initial dose to try a different shot.

The clinical considerations for heterologous mixing are as follows:

  • The same product that was used for the primary regimen should be used for the booster
    • If that is not available or another product is preferred, heterologous boosting with a single dose of any of the authorized COVID-19 vaccine boosters is acceptable
  • Heterologous dosing may be considered for the booster dose only
  • Individual benefit-risk assessment may inform which booster product to use

When will the general public be able to get a booster shot?

All eligible individuals are currently able to get a booster shot.

Why do I need a booster shot?

While the COVID-19 vaccines currently authorized in the U.S. continue to be effective in reducing the risk of severe disease, hospitalization and death, including protection against the Delta variant, many vaccines see reduced protection over time.   At this time, certain individuals who received a two-dose Pfizer-BioNTech COVID-19 vaccine series may receive a booster shot to protect themselves as the primary series wanes over time.

Where can I get an additional dose or a booster shot?

Many vaccine providers, such as local health departments, clinics, and pharmacies, are able to provide additional doses or booster doses. You can find a vaccine provider at or call 1-800-232-0244 (TTY 888-720-7489).

Should an immunocompromised person who gets the additional dose also get a booster dose 6-months later?

At this time, a booster shot is not recommended after an additional dose.