A healthcare worker will administer a third dose of the Pfizer BioNTech Covid-19 vaccine at a senior citizens’ home in Worcester, Pennsylvania, USA on Wednesday, August 25, 2021.

Hannah Beier | Bloomberg | Getty Images

Side effects of Covid vaccine booster shots are similar to those after the second dose and more likely to affect younger people, Pfizer said in new data submitted to the Food and Drug Administration to approve the distribution of booster shots in the U.S. obtain

Pfizer’s Phase III vaccine booster dose study, which enrolled a group of approximately 300 participants ages 18 to 55, found that 63.7% experienced fatigue, 48.4% headache, and 39% after receiving their booster vaccinations , 1% had muscle pain. Most of the reactions to the booster have been mild or moderate, the company said in a 52-page report released by the agency on Wednesday. The company is working with BioNTech to seek emergency approval from the FDA to give a third dose of its vaccine to people aged 16 and over in the United States

Pfizer previously examined side effects in 2,682 recipients of the second dose aged 16 to 55 years and found that 61.5% developed fatigue, 54% had a headache, and 39.3% had muscle pain.

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

There were no reported cases of anaphylaxis, hypersensitivity, Bell’s palsy, appendicitis, myocarditis, or pericarditis among phase three participants, the report said. Pfizer added that it had not discovered any new adverse drug reactions related to the booster.

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

President Joe Biden has announced that it will begin distributing booster vaccinations by September 20, but the FDA declined on Wednesday to comment in support of Pfizer’s Covid boosters. The agency has not yet independently verified the data and conclusions from studies of the effectiveness of Pfizer’s boosters, according to an FDA report.