Side Effects From Covid Vaccine Boosters Are Similar to Second Dose, Pfizer Tells FDA

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  • Side effects from its Covid vaccine booster shots are similar to those felt after the second dose, Pfizer said in new data submitted to the FDA.
  • The side effects are more likely to affect younger people, the company's research showed.
  • Pfizer is seeking approval to distribute its booster shots across the U.S.

Side effects from Covid vaccine booster shots are similar to those felt after the second dose and are more likely to affect younger people, Pfizer said in new data submitted to the Food and Drug Administration as it seeks approval to distribute booster shots across the U.S.

Pfizer's phase three study of vaccine booster doses, which included a group of about 300 participants from ages 18 to 55, found that 63.7% experienced fatigue after getting their boosters, 48.4% had headaches and 39.1% felt muscle pain. The majority of reactions to the booster were mild or moderate in severity, the company said in a 52-page report released by the agency Wednesday. The company, along with BioNTech, are seeking the FDA's emergency approval to administer third doses of its vaccine to people 16 and over across the U.S.

Pfizer previously evaluated side effects on 2,682 second-dose recipients ages 16 to 55 and found that 61.5% developed fatigue, 54% suffered headaches and 39.3% dealt with muscle pain.

The study also tracked adverse events among 306 booster recipients, 44 of whom developed at least one unexpected side effect. The most common adverse event, swelling of the lymph nodes, appeared in 16 of the participants.

There were no reported cases of anaphylaxis, hypersensitivity, Bell's palsy, appendicitis, myocarditis or pericarditis among the phase three participants, the report said. Pfizer added that it failed to discover any new adverse drug reactions linked to the booster.

The report also found that 29.1% of booster recipients experienced chills, while 25.3% felt joint pain. Reports of fever dropped by half between the second and third dose: 16.4% of participants in the second dose study reported fever symptoms, compared with 8.7% of those in the booster study.

President Joe Biden has said he plans to begin distributing booster shots by Sept. 20, but the FDA on Wednesday declined to take a stance on supporting Pfizer's Covid boosters. The agency has not yet independently verified the data and conclusions from studies on the effectiveness of Pfizer's boosters, an FDA report said.

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