Frequently Asked Questions About the COVID-19 Vaccine Third Dose and Booster Shot

The FDA has authorized a third dose of an mRNA COVID-19 vaccine for individuals who have undergone solid organ transplantation, or who are diagnosed with conditions that are considered to have an equivalent level of immunocompromise. Patients who are not immunocompromised and caregivers who take care of patients who are immunocompromised should not get a third dose of the COVID vaccine at this time.

Updated: September 29, 2021

While COVID-19 vaccination remains extremely effective in preventing severe disease, studies show that after getting vaccinated against COVID-19, protection against the virus may decrease over time and be less able to protect against the Delta variant.

For those who are severely immunocompromised, there has been research showing that an additional dose is required for optimal immunity against severe disease from COVID-19. And recently the CDC has recommended that certain groups of people receive a COVID-19 booster shot.

Below are a few common questions about the newly recommended booster shot for some people and the additional dose for those who are severely immunocompromised.

Is the booster shot the same as a third dose?


A COVID-19 booster shot is given to extend protection against COVID-19 in fully vaccinated individuals who are not severely immunocompromised.

A third or additional COVID-19 vaccine dose for those who are immunocompromised is intended for vaccinated people who have severely weakened immune systems because of health conditions or medical treatments to help them develop immunity to COVID-19.

Based off of studies that evaluated the immunity of immunocompromised individuals after receiving two doses of an mRNA COVID-19 vaccine, it was found that these individuals did not reach optimal levels of protection.

Therefore, it is recommended that immunocompromised individuals receive a third or additional dose of the same mRNA COVID-19 vaccine (Moderna or Pfizer-BioNTech) at least 28 days after receiving their second dose to bring their levels up to an optimal level of protection.

Am I eligible to receive a COVID-19 booster shot?

According to CDC guidelines, to be eligible to receive a booster dose of the Pfizer COVID-19 vaccine, you must already have received two doses of the Pfizer-BioNTech vaccine at least six months ago and meet the following mandated criteria:

  • Are 65 years of age or older, or
  • Are 18-64 years of age and have an underlying medical condition that puts you at high risk of severe COVID-19, or
  • Are 18-64 years of age at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting

Those who are fully vaccinated with the Moderna or J&J vaccine will need to wait until further federal guidance is released regarding booster shots of those two vaccines.

Learn more about these eligibility criteria for the COVID-19 booster shot.

How do I know if I need a third or additional dose of the COVID-19 vaccine?

According to CDC guidelines, patients with the following conditions should receive a third or additional dose of the COVID-19 vaccine at least 28 days following the two-dose regimen of the same mRNA vaccine (Moderna or Pfizer-BioNTech):

  • Been receiving active cancer treatment for tumors or cancers of the blood.
  • Received an organ transplant and are taking medication to suppress the immune system.
  • Have either had a stem cell transplant within the last two years or are taking medicine to suppress the immune system
  • Were diagnosed with DiGeorge syndrome or Wiskott-Aldrich syndrome
  • Are diagnosed with advanced or untreated HIV infection
  • Are taking drugs such as high-dose steroids or other medications that may cause severe suppression of the immune system
  • Been receiving chronic hemodyalysis

If I received a third dose, do I still need a booster shot?

If you received a third or additional dose of the Pfizer-BioNTech COVID-19 vaccine, it has not yet been determined if a booster shot will be needed. 

Where can I receive my booster shot?

At this time, there is sufficient COVID-19 vaccine supply in the community. If you meet the eligibility criteria listed above for a COVID-19 booster shot, we encourage you to schedule an appointment at your local pharmacy or a retail pharmacy chain.

Where can I receive a third dose of the COVID-19 vaccine?

The third dose is intended for severely immunocompromised patients.

If you meet the eligibility criteria listed above for a third dose of the COVID-19 vaccine, you can schedule an appointment at your local pharmacy or retail pharmacy chain.

Temple Health will also continue to provide third doses of the COVID-19 vaccine to our immunocompromised patients. To schedule an appointment for a third dose, you can call 215-707-6999.

How will Fox Chase know if I get vaccinated elsewhere?

At your next appointment, please inform our medical team that you have received either the third dose (if you are immunocompromised) or a booster shot so that we can be sure to include it as a part of your record.

Are there side effects from the booster shot?

The most commonly reported side effects by clinical trial participants who received a booster dose of the vaccine were pain, redness, and swelling at the injection site, as well as fatigue, headache, muscle or joint pain and chills.

Swollen lymph nodes in the underarm were observed more frequently following the booster dose than after the primary two-dose series.

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