Many people experience pain at the site of injection, fatigue, muscle pain or headache. Data from the Pfizer/BioNTech and Moderna trials also show the side effects included joint pain, chills or fever. These reactions are more likely after the second dose of those vaccines, given several weeks after the first, and are more common and severe in younger people. The Johnson & Johnson side effects, too, were more common in 18- to 59-year-old participants.
Since the rollout of the vaccines, a small number of people in the U.S. have had serious allergic reactions following receipt of the shots. In addition, the Centers for Disease Control and Prevention and the Food and Drug Administration announced on April 13 that they are investigating six reported cases of “a rare and severe type of blood clot” out of the 7.2 million individuals who have received the Johnson & Johnson vaccine in the U.S., as of April 12.
The CDC has advised that anyone who has previously experienced anaphylaxis or had any kind of immediate allergic reaction to any vaccine or injection be monitored for a half hour after getting the shot.
The FDA recommends against vaccination for those who have had a serious allergic reaction to a previous dose of either the Pfizer or Moderna vaccine or one of the ingredients of any of the authorized vaccines.