Pharmacists offering COVID-19 boosters often are asked if the third dose of the Pfizer-BioNTech vaccine results in similar side effects as the first two.

In early research from the CDC that looked at 306 Pfizer-BioNTech clinical trial participants, adverse reactions after Dose 3 were generally similar to those after Dose 2, according to an article in Morbidity & Mortality Weekly Report.

In addition, the authors from the CDC's COVID-19 Response Team state that from August 12 to September 19, among 12,591 v-safe registrants who completed a health check-in survey after all three doses of an mRNA COVID-19 vaccine, 79.4% and 74.1% reported local or systemic reactions, respectively, after the third dose, and 77.6% and 76.5% reported local or systemic reactions, respectively, after the second dose. V-safe is a smartphone-based tool that uses text messaging and Web surveys to give personalized health check-ins after the patient receives a COVID-19 vaccine.

The CDC notes that, as of mid-September, about 2.21 million people in the United States had received additional doses of COVID-19 vaccines after completing a primary series.

"During August 12-September 19, 2021, no unexpected patterns of adverse reactions were observed among 22,191 v-safe registrants who received an additional dose of COVID-19 vaccine," the authors write. "Most reported local and systemic reactions were mild to moderate, transient, and most frequently reported the day after vaccination. Most registrants who received an additional dose reported a primary mRNA vaccination series followed by a third dose from the same manufacturer."

An analysis of v-safe data found that local reactions were slightly more common and systemic reactions somewhat less common after Dose 3 of the Pfizer-BioNTech vaccine, however. Among 12,591 (58.1%) v-safe registrants who completed at least one health check-in survey on Days 0 to 7 after all three doses, 79.4% and 74.1% 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.

Among registrants who received three doses of Moderna (6,283), local reactions were reported more frequently after Dose 3 than after Dose 2 (5,323; 84.7% and 5,249; 83.5%; P = .03), whereas systemic reactions were reported less frequently. Registrants who received three doses of Pfizer-BioNTech (6,308) also reported that local reactions occurred more frequently after Dose 3 than after Dose 2 (4,674; 74.1% and 4,523; 71.7%; P <.001) and that systemic reactions were less frequent.

No conclusions were possible on what happened when recipients received an additional dose from a manufacturer other than that of their primary series or had received a second dose of the Janssen vaccine, according to the report, because the numbers were so small.

The CDC's Advisory Committee on Immunization Practices (ACIP) recommends that Americans with moderately to severely immunocompromising conditions receive a third dose of mRNA COVID-19 vaccine from the same manufacturer as their primary series. The CDC recommendations for an additional dose do not currently include patients who received the Janssen vaccine.

During the time covered by this study, ACIP recommendations for an additional dose of COVID-19 vaccine were limited to patients with moderately to severely immunocompromising conditions who had received two doses of an mRNA vaccine.

Now, the CDC recommends an additional dose of Pfizer-BioNTech vaccine 6 or more months after completion of the primary vaccine series in persons aged 65 years or older who live in long-term care settings. People aged 50 to 64 years with underlying medical conditions, those aged 18 to 49 years with underlying medical conditions, and those aged 18 to 64 years who are at increased risk for COVID-19 exposure and transmission because of their occupational or institutional setting also can opt to receive an additional dose based on their individual benefits and risks.

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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