There have been 275 cases of myocarditis or pericarditis, a heart inflammation condition, recorded in 16-24 year-olds after they received their second shot of the coronavirus vaccine.
The CDC cited preliminary data from its vaccine safety monitor system, and found the cases were higher than they expected, having previously assumed cases might occur but would only be in the double digits.
81% of the patients were hospitalized, but the majority have recovered, CNBC reported. Three were in intensive care.
The majority of the inflammation cases have been recorded in men, and symptoms occur two to three days after the second dose. There have been 475 cases in people ages 30 and younger, out of the roughly 141 million Americans who have been fully vaccinated.