This week, the Food and Drug Administration authorized a second booster dose of the Pfizer/BioNTech or the Moderna COVID-19 vaccines for people 50 and older and certain immunocompromised individuals. Emerging evidence suggests that a second booster dose of an mRNA COVID-19 vaccine improves protection against severe COVID-19 and is not associated with new safety concerns. The second booster can be administered at least four months after receipt of a first booster dose.