COVID-19 Booster Dose: Frequently Asked Questions

Since before COVID-19 vaccines were made available, there has been speculation on if initial vaccination would be sufficient or if there would be recommendations for yearly vaccination, like the flu shot. As the vaccines continue to be studied and more information about COVID-19 becomes available, every effort is being made to ensure that you have the information and tools necessary to protect yourself from COVID-19 infection. Based on the data available, the FDA has recently authorized an additional dose or booster dose of certain COVID-19 vaccines for patients meeting specific criteria. At this time, only one COVID-19 booster dose is recommended. 


The term “booster” is used to describe an additional dose of a vaccine that is given to boost your immune system. The booster shot helps you to maintain immunity and keep you protected against COVID-19 after the immunity from the first two doses begins to naturally decrease over time.1


Studies have shown that COVID-19 vaccines are effective at preventing severe disease and reducing the risk of hospitalization, but protection against the virus may decrease over time. This is due to natural waning of immunity, which is why a booster dose is needed.2 Other routine vaccinations, such as the tetanus shot, require booster doses for the same reason. A booster dose triggers a memory response within your immune system so that your immune system is able to respond quickly if you are ever exposed to the virus.1 With the emergence of COVID-19 variants that are highly infectious, such as the Delta variant, it is extremely important to maintain immunity, which can be done through a booster dose. One study on the Pfizer-BioNTech vaccine showed that a booster dose increased patients’ immune response, which provides increased protection against COVID-19, including variants.2


The FDA has authorized the Pfizer booster dose for those meeting certain eligibility criteria as listed in the next section. For patients meeting this criteria, the booster dose can be given at least 6 months after the second dose. 2  

For patients with moderate to severe immunocompromising conditions, such as those listed in the next section, the FDA has authorized a third dose of Pfizer and Moderna. For these patients, the third dose can be given at least 28 days after the second dose. This additional dose is given sooner because patients with weakened immune systems are more likely to have severe illness if infected with COVID-19 and are less likely to develop sufficient immunity after only two doses of the vaccine.3

Currently, an additional dose of Moderna is only authorized for immunocompromised patients and not yet available for others. The Johnson & Johnson COVID-19 vaccine has not not been authorized for booster doses.

The FDA is consistently reviewing data on COVID-19 vaccines, and booster doses that are not currently available for patients who do not meet the following criteria may become available at a later date. 


According to the CDC, you should get the Pfizer booster dose if you have completed the 2-dose Pfizer series at least 6 months ago and fall into one of the categories below:

  • 65 years of age or older
  • 50-64 years old with underlying medical conditions (obesity, asthma, heart disease, high blood pressure, diabetes)
  •  A resident of a long-term care facility and at least 18 years old

If you do not meet the above criteria but would like to get a booster dose, you may get the Pfizer booster dose at least 6 months after completing the 2-dose Pfizer series if you fall into one of the categories below:

  • 18-49 years old with underlying medical conditions (obesity, asthma, heart disease, high blood pressure, diabetes)
  • 18-64 years old and working in a high-risk setting where you may be exposed to COVID-19 (healthcare workers, first responders, teachers, retail and restaurant workers, public transportation workers, etc.)
  • 18-64 years old and living in a high-risk setting where you may be exposed to COVID-19 (correctional facilities, homeless shelters, college dorms, any group living setting).2,4

If you have one of the following immunocompromising conditions, you should get a third dose of Pfizer or Modera at least 28 days after completing the 2-dose series:

  • Active cancer
  • Organ transplant and taking medication to suppress the immune system
  • Stem cell transplant within past 2 years or currently taking medication to suppress the immune system
  • Advanced or untreated HIV
  • Active treatment with medications that suppress the immune system.3,4


The CDC currently recommends that any additional dose match the vaccine that you initially received. This means that if you completed the 2-dose Pfizer series, your next dose should be the Pfizer vaccine, but if you completed the 2-dose Moderna series, your next dose should be the Moderna vaccine. Some exceptions do exist where your next dose could be different than what you previously received. If you are unsure of which vaccine you should be getting for your booster dose, please contact your doctor or pharmacist.3  


At this time not everyone has been made eligible for a booster dose of the COVID-19 vaccine. However, it is important to stay alert to changes in eligibility as new information is made available often. If you have any questions about eligibility or updates in the media, reach out to your doctor or pharmacist to get the most accurate information. In the meantime, it is important to continue safe practices as recommended by the CDC which include wearing a mask, frequent hand washing, avoiding crowds, and practicing social distancing.5    


  1. Will you need a COVID-19 booster? What we know so far. Published July 27, 2021. Updated September 24, 2021. Accessed October 4, 2021. 
  2. Who is eligible for a COVID-19 vaccine booster shot? Updated September 30, 2021. Accessed October 4, 2021. 
  3. COVID-19 vaccines for moderately to severely immunocompromised people. Updated September 2, 2021. Accessed October 4, 2021. 
  4. COVID-19 vaccine boosters and additional doses. Accessed October 4, 2021.
  5. COVID-19 and your health. Centers for Disease Control and Prevention. Updated 2021. Accessed September 30, 2021.