Fifteen children, many of whom had the coronavirus, have recently been hospitalized in New York City with a mysterious syndrome that doctors do not yet fully understand but that has also been reported in several European countries, health officials announced on Monday night.

Many of the children, ages 2 to 15, have shown symptoms associated with toxic shock or Kawasaki disease, a rare illness in children that involves inflammation of the blood vessels, including coronary arteries, the city’s health department said.

None of the New York City patients with the syndrome have died, according to a bulletin from the health department, which describes the illness as a “multisystem inflammatory syndrome potentially associated with Covid-19.”