COVID-19 Vaccine Booster Doses vs. Third Doses: What’s the Difference?

October 11, 2021


Pader Moua, MPH
Policy Analyst

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COVID-19 booster shots and third doses are now available for certain individuals. This has led some people to ask: What’s the difference? Our new infographic explains.

As of Monday, Oct. 11, over 74,000 Arkansans had received either a booster or a third dose of the COVID-19 vaccine. Currently, the Pfizer vaccine is authorized for both booster and third doses, and the Moderna vaccine is authorized only for third doses. The Johnson & Johnson vaccine is not currently authorized for either booster or third doses.

Booster doses are only authorized for certain recipients of the Pfizer vaccine who had their second dose at least six months ago. These doses are meant to provide additional protection for certain vulnerable populations and people who live or work in high-risk settings, as protection against COVID-19 may wane over time. These individuals include those who are:

Third doses are authorized for recipients of the Pfizer and Moderna vaccines who have moderate-to-severe immunocompromised systems. These individuals can receive their third dose at least 28 days after their second dose. Third doses are “intended to improve immunocompromised people’s response to their initial vaccine series.” Individuals eligible for a third dose include 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 two years or are taking medicine to suppress the immune system
  • moderate or severe primary immunodeficiency, such as DiGeorge syndrome or Wiskott-Aldrich syndrome
  • advanced or untreated HIV infection
  • active treatment with high-dose corticosteroids or other drugs that may suppress their immune response