Shawn Evans, attending emergency physician and director of resuscitation at Scripps Memorial Hospital La Jolla, said he and other doctors on the front lines of the epidemic have been “humbled” by how many young people have been hospitalized and ended up in the ICU during the outbreak.

“This is nothing like we had predicted based on the data from these other countries,” Evans, who estimated roughly half the covid-19 patients in his ICU have been under 50, said in an interview.

Evans said the vast majority of young people who contract the disease fare well and recover. But for a minority, it appears to cause a unique change in the blood’s oxygen-carrying hemoglobin cells.

“Young people who are otherwise fit can tolerate this longer, but at the expense of their heart and their pulmonary functions,” said Evans, who likened some of the symptoms in younger people to prolonged carbon monoxide exposure.