Side effects from Covid 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 3 study of booster doses, which included a group of about 300 participants from 18 to 55 years old, 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 on Wednesday. The company, along with BioNTech, are seeking the FDA’s emergency approval to administer third doses 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.