Dose 3 Adverse Reactions Similar to Dose 2

October 1, 2021

This morning, the CDC released their Morbidity and Mortality Weekly Report focusing on third doses of the COVID-19 vaccine. The report referenced Pfizer’s Phase 3 clinical trial, which included 306 participants, ages 18-55, who received a booster dose. Doses were administered 5-8 months after completion of a primary series using mRNA vaccines. Adverse reactions were similar to those after the second dose, and “included mild to moderate injection site and systemic reactions” (1).

V-safe was developed by the CDC as a voluntary, self-reporting surveillance system for “local injection site and systemic reactions and health impacts” post-vaccination. From August 12 – September 19, 2021, over 22,000 registrants reported getting a third dose of the COVID-19 vaccine into v-safe. Over 97% reported getting a mRNA vaccine for their primary series, followed by a third dose of the same vaccine. “Voluntary reports to v-safe found no unexpected patterns of adverse reactions after an additional dose of COVID-19 vaccine.” Of those who completed check-ins for all three doses, 79.4% and 74.1% reported local or systemic reactions, respectively, after their third dose. 77.6% and 76.5% reported local or system reactions following their second dose. Moreover, the majority of adverse reactions were mild or moderate in nature.

Safety and efficacy data on mix-and-matching doses from different manufacturers is still limited.