U.S. Centers for Disease Control and Prevention.Side effects from the vaccines being used in the U.S., developed by Moderna and Pfizer-BioNtech, are normal signs your body is building protection.
The CDC says flu-like symptoms are to be expected and can include fever, chills, headache, muscle aches and tiredness. Some may have pain and swelling in the arm at the site of the injection.
All side effects should go away within a few days.In vaccine trials for Moderna and Pfizer, side effects were more frequent after the second dose.
Moss said some may have had minimal or no symptoms from the first dose, but will feel side effects after the second because their immune system is already primed — resulting in a more intense inflammatory reaction.