No unexpected patterns of adverse reactions were identified following receipt of a third dose of COVID-19 vaccine, according to findings published in a recent Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report.

During the period of August 12 to September 19, 2021, a total of 22,191 individuals reported receiving an additional dose of a COVID-19 vaccine following a primary series to v-safe, a voluntary US safety surveillance system. Of these people, 31.8% reported health impacts, with 28.3% stating they were unable to perform normal daily activities, most often on the day after vaccination.

Adverse event profiles were then compared among the 12,591 individuals who completed a health check-in survey after all 3 doses of the same mRNA COVID-19 vaccine. Findings showed that 79.4% and 74.1% of v-safe registrants reported local or systemic reactions, respectively, after dose 3, compared with 77.6% and 76.5% who reported local or systemic reactions, respectively, after dose 2.

Local reactions were reported more frequently after the third dose of the Moderna COVID-19 vaccine than after the second (P =.03); however, systemic reactions were reported less frequently (P <.001). Similarly, among individuals who received 3 doses of the Pfizer-BioNTech COVID-19 vaccine, local reactions occurred more frequently (P <.001) and systemic reactions less frequently (P <.001) with the third dose vs the second dose.

“Voluntary reports to v-safe found no unexpected patterns of adverse reactions after an additional dose of COVID-19 vaccine,” the report authors concluded, adding that the CDC will continue to monitor and report on the safety of additional COVID-19 vaccine doses.


Hause AM, Baggs J, Gee J. et al. Safety monitoring of an additional dose of COVID-19 vaccine-United States, August 12-September 19, 2021. MMWR Morb Mortal Wkly Rep. Published online September 28, 2021. icon.