There have been more than 1,200 cases of a rare heart inflammation condition in people who received Pfizer‘s or Moderna’s Covid-19 vaccine, according to a CDC presentation slide published Wednesday ahead of an advisory meeting.

The CDC’s Advisory Committee on Immunization Practices is holding a meeting to discuss rare, but higher-than-expected, reports of myocarditis or pericarditis in 16- to-24-year-olds after receiving the mRNA vaccines. Myocarditis is the inflammation of the heart muscle, while pericarditis is the inflammation of the membrane surrounding the heart.

This is a developing story. Please check back for updates.