Most children admitted to intensive care with a serious inflammatory complication after getting Covid-19 didn’t have serious lingering issues a year later, according to a study of data collected from hospitals across the U.K.

As the highly contagious Delta variant sweeps across the world, doctors say they are worried about its effect on children, especially those who are unvaccinated. In some parts of the U.S., more children have been hospitalized for Covid-19 treatment recently than at any time during the pandemic since U.S. authorities began tracking the data last year.

The U.K. study tracked the health of children with multisystem inflammatory syndrome, or MIS-C, a rare condition that can occur in children several weeks after Covid-19 infection. It can involve many different organ systems and lead to issues with the heart, including aneurysms in the coronary arteries, arrhythmias and problems with heart function.

Without the proper diagnosis and management, which often involves the use of intravenous immune globulin or corticosteroids, MIS-C can lead to organ damage or even death. More than 4,400 cases of MIS-C were reported among children in the U.S. during the pandemic as of the end of July, according to the Centers for Disease Control and Prevention.

Most children seemed to recover from MIS-C without any serious long-term problems, according to researchers in the U.K. who collected data on 68 patients under the age of 18 admitted to intensive-care units with MIS-C before May 10, 2020.