A “booster dose” is another dose of a vaccine that is given to someone who built enough protection after vaccination, but then that protection decreased over time (this is called waning immunity). The Centers for Disease Control and Prevention has recommended booster doses of Pfizer vaccine to people 18 years and older who completed the Pfizer COVID-19 vaccine as their primary series, and it has been AT LEAST six months since receiving the second dose.

The CDC recommends the booster for the following eligible individuals:

• People 65 years and older and residents in long-term care settings should receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series
• People age 50–64 years with underlying medical conditions should receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series
• People aged 18–49 years with underlying medical conditions may receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series, based on their individual benefits and risks
• People aged 18-64 years who are at increased risk for COVID-19 exposure and transmission because of occupational or institutional setting may receive a booster shot of Pfizer-BioNTech’s COVID-19 vaccine at least 6 months after their Pfizer-BioNTech primary series, based on their individual benefits and risks.

Only the Pfizer vaccine is authorized by the Food and Drug Administration for a booster dose.