>> imagine trying to treat severe bacterial pneumonia without antibiotics. we're basically relying on a machine and the patient's own immune system to recover. >> other area hospitals also overwhelmed, like morristown medical in new jersey where dr. lewis rubinson works. >> our numbers went up pretty dramatically, pretty quickly. we ultimately had 20 units with covid patients. our maximum census because over 300 patients concurrently. >> reporter: one study of a new york city health system found that in march, 25.6% of hospitalized covid-19 patients would end up dying. imagine that. 1 in 4. >> this is a terrible, very terrible virus. and it's killing our people. >> by june, that mortality rate had dropped by more than two-thirds to 7.6%. >> the number of deaths has not been increasing markedly.