Third Dose of mRNA COVID-19 Vaccines Recommended for Moderately to Severely Immunocompromised People

According to the Centers for Disease Control and Prevention (CDC), people who have moderately to severely compromised immune systems should receive an additional dose of mRNA COVID-19 vaccine (Moderna or Pfizer-BioNTech) following the initial two doses. The third dose should be administered at least 28 days after the second dose. A third dose is recommended because people who are immunocompromised are more vulnerable and are at a higher risk of having a serious illness from COVID-19.

If you received the Janssen/Johnson & Johnson one-dose COVID-19 vaccine, experts are not recommending any additional COVID-19 vaccinations at this time.

Who should get a third dose?

A third dose is recommended for 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 2 years or are taking medicine to suppress the immune system
  • Moderate or severe primary immunodeficiency (such as DiGeorge syndrome, Wiskott-Aldrich syndrome)
  • Advanced or untreated HIV infection
  • Active treatment with high-dose corticosteroids or other drugs that may suppress your immune response

How do I get my third dose?

If you are a Dartmouth Hitchcock patient with an established primary care provider (PCP) or a specialty care provider and meet the criteria above, please contact your provider’s office to request a third dose.

Please have your COVID-19 vaccination card handy so that you can confirm the date of your second dose and whether you received the Pfizer-BioNTech vaccine or the Moderna vaccine (the third dose will be with the same vaccine).

Your provider will then review your request. If you meet the criteria, your provider will put in an order for a third dose of vaccine for you. The office will contact you to schedule your vaccination appointment, generally within 5 business days.

The mRNA vaccines (Moderna and Pfizer-BioNTech) are also widely available at local pharmacies and other vaccination sites.


As always, we strongly recommend that you continue to take precautions to protect yourself from COVID-19, even after a third dose of the vaccine. This includes wearing your face mask when in public indoor places (like a grocery store) or in large groups (outside and inside). It is also important to continue to wash your hands, or use alcohol-based hand sanitizer, frequently and to maintain 6 feet of physical distance when possible.

For more information on the COVID-19 vaccine visit, please refer to our COVID-19 Vaccine Updates web page.

Third dose frequently asked questions

What is the difference between a third dose and a booster shot?

A third dose of the mRNA vaccine is being recommended for people who have weakened immune systems. This is because they didn't get an adequate immune response from the first two doses.

A “booster dose” is a supplemental vaccine dose given to people when the immune response to a primary vaccine series was adequate but is likely to have decreased over time. For more information, see the Booster Shots FAQ.

What should I do if I'm immunocompromised and received the Janssen/Johnson & Johnson COVID-19 vaccine?

According to the CDC, there is not enough data at this time to determine whether immunocompromised people who received the Janssen/Johnson & Johnson COVID-19 vaccine will require an additional vaccination. Studies are currently in progress, and we will share updates as soon as available.

When should I get a third dose?

People who are moderate to severely immunocompromised are recommended to get their third dose at least 28 days after their second dose of an mRNA vaccine (Pfizer-BioNTech or Moderna).

Does my third dose need to be the same brand as my initial vaccines?

Yes. The CDC recommends that the third dose be the same brand as the other mRNA vaccines you received earlier this year (Moderna or Pfizer-BioNTech).

Do I need a note from my provider if I get my vaccine at a retail pharmacy?

If you go to a retail pharmacy or another vaccination site (such as CVS or Walgreens), you do not need a provider's note to get your third dose. You will just need to tell the retail location that you are immunocompromised.

Where can I get another dose of Pfizer-BioNTech or Moderna vaccine?

The COVID-19 vaccines are widely available at this time. To find the closest vaccine, you can visit:

You can also text your zip code to 438829 or call 800-232-0233 to find a location.