According to findings from a report published in October 2021 in the Centers for Disease Control and Prevention (CDC) Morbidity and Mortality Weekly Report, no unexpected patterns of adverse reactions were identified following the receipt of a third dose of messenger RNA (mRNA vaccine).

 During the period of August 12, 2021, 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, smartphone U.S. safety surveillance system for vaccinated eligible persons to provide information on adverse reactions after COVID-19 vaccination. The CDC noted that, of these individuals, 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 persons who completed a health check-in survey after all three doses of the same mRNA COVID-19 vaccine. The findings also 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). Likewise, among persons who received three doses of the Pfizer-BioNTech COVID-19 vaccine, local reactions happened more frequently (P <.001), and systemic reactions occurred less frequently (P <.001) with the third dose versus the second dose.

In the CDC report, the authors wrote that the findings in this report are subject to at least four limitations. First, enrollment in v-safe is voluntary and likely not representative of the vaccinated U.S. population; the majority of participants identified themselves as white and non-Hispanic.

Second, during this study period, additional dose recommendations were limited to persons with immunocompromising conditions who completed a primary mRNA COVID-19 vaccination series; however, v-safe does not include information about immune status. Additional-dose recipients likely include individuals with and without immunocompromising conditions.

Third, a causal relationship between a vaccine and a clinically serious adverse event reported after vaccination cannot be confirmed using v-safe data.

Finally, insufficient data were available to establish patterns of adverse reactions after receipt of an additional dose from a manufacturer different from the primary series or for the Janssen vaccine.

The authors stated, "Voluntary reports to v-safe found no unexpected patterns of adverse reactions after an additional dose of COVID-19 vaccine." They also indicated that the CDC will continue to monitor and report on the safety of additional COVID-19 vaccine doses. The CDC also noted the additional data on adverse reactions associated with different combinations of vaccines, and time since completion of primary series will be critical to guide public health recommendations.

The content contained in this article is for informational purposes only. The content is not intended to be a substitute for professional advice. Reliance on any information provided in this article is solely at your own risk.

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