What are the common side effects of the Pfizer COVID-19 vaccine that I may experience?

Persons less than 55 years of age appear to experience a slightly higher rate of side effects after receipt of the vaccine. About 80% of younger participants and 70% of older participants reported pain at the injection site. This was not significantly different between dose 1 and dose 2. Other local reactions included redness and swelling at the injection site (about 5% each). Only 0.6% of participants reported severe local reactions.

Systemic reactions were also generally mild to moderate in severity. Most began 1 or 2 days after receipt of the vaccine and resolved within 1 day after they began. Participants great than 55 years generally experienced similar reactions to the younger group but at a lower rate. Systemic reactions were more common after the second dose.