How Is The Third Dose Of A COVID-19 Vaccine Different From A Booster?

On August 13, the Food and Drug Administration and the Centers for Disease Control and Prevention came to an agreement to authorize emergency use for a third dose of the COVID-19 vaccine for immunocompromised people (via New York Times). A third dose of the Pfizer-BioNTech or Moderna vaccine is now recommended for a small group of people who may be more vulnerable to serious bouts of COVID-19. This includes people who have received an organ transplant, people who are actively receiving cancer treatments that affect the immune system, people with advanced HIV, and a few other health scenarios (via UChicago News).

"Increasingly, research shows many people who have weakened immune systems haven't been able to receive full protection from their COVID-19 vaccines," Associate Professor Emily Landon of University of Chicago Medicine said. "Unlike healthy people who've been vaccinated against SARS-CoV-2, the virus that causes COVID-19, immunocompromised people's bodies may not produce enough protective antibodies after two doses of the COVID-19 vaccines."

The only difference between a third dose of the COVID-19 vaccine and a booster shot is the reason behind why someone is getting the respective shot. The term "booster" is used to describe a vaccine dose offered to people who developed an adequate immune response from the initial vaccine but have had their protection decrease slightly over time. A third dose is given to people who did not develop a strong enough immune response from the initial vaccine.