As corona virus cases surge and hospital beds fill throughout Southern California, one of the few tools that doctors have to treat the disease —plasma from recovered COVID-19 patients— is in alarmingly short supply. Hospitals and blood banks in Orange County, Los Angeles, Riverside and San Bernardino beseech recovered patients to donate blood so their antibodies can help treat the sick. “Hoag Hospital is putting out an urgent request for plasma donors.” spokeswoman ​Chelsea Kottke said. “As the number of patients with COVID-19 continues to climb in Orange County, our need for convalescent plasma also increases and the amount left available is very limited.”