In the United States, 74.9% of patients experienced local side effects after receiving their third Covid-19 vaccine, while 69.6% suffered from systemic reactions. On August 12, 2021, the U.S. Food and Drug Administration (FDA) approved a Covid-19 vaccine booster shot for people with moderate to severe immune deficiencies using the vaccines from Biontech/Pfizer and Moderna. As of September 19, 2021, approximately 2.2 million people had received their third dose. However, the manufacturers have only tested the vaccine’s side effects on relatively few participants, raising concerns about the safety of the booster.
To address these concerns, the Centers for Disease Control and Prevention (CDC) in the U.S. allowed vaccinated patients to report their experiences with the third Covid-19 vaccine through an app. According to the analysis of the data obtained from the app, published in the Morbidity and Mortality Weekly Report, the booster did not cause a significant increase in antibody titers, which would have led to more side effects. At the time of the analysis, 22,191 patients had reported their experience with the third Covid-19 vaccine through the app. The booster was administered a median of 182 days after the second dose. Nearly three-quarters (74.9%) reported local side effects such as pain at the injection site (71%). Systemic reactions also occurred in a majority of patients (69.9%), with fatigue (56%) and headaches (43.4%) being the most common.
The local side effects increased from 71.7% after the second dose to 74.1% after the third dose for the Biontech/Pfizer vaccine BNT162b2. However, there was a decrease in systemic side effects from 71.7% to 69.2%. For the Moderna vaccine mRNA-1273, the local side effects increased from 83.5% to 84.7%, while the systemic side effects decreased from 81.3% to 79%. Overall, the authors of the study concluded that the booster’s tolerability was not worse than that of the first and second vaccine doses.
