The largest analysis of hospitalized U.S. Covid-19 patients to date finds that most did not survive after being placed on a mechanical ventilator.

The study done by the Northwell Health Covid-19 Research Consortium included that the health records of 5,700 COVID-19 patients hospitalized between March 1st and April 4th at facilities overseen by Northwell Health, New York State’s largest health system.

Among the 2,634 patients for whom outcomes were known, the overall death rate was 21%, but it rose to 88% for those who received mechanical ventilation.