The Adverse Reactions of Pfizer BioNTech COVID-19 Vaccine Booster Dose are Mild and Similar to the Second Dose Responses: A Retrospective Cross-Sectional Study.

Background: Like other vaccines, Pfizer BioNTech's COVID-19 vaccine efficacy against SARS-CoV-2 virus infections begins to decline within a few months after the 2 dose. On August 12, 2021, the FDA allowed additional Pfizer BioNTch's COVID-19 vaccine dose (3 or booster dose) for individuals with weakened immunity. This study aimed to evaluate the short-term adverse reactions (ADRs) of the 2 and the 3 doses of the Pfizer BioNTech COVID-19 vaccine.