COVID-19 patients had an in-hospital death rate two times higher than that of influenza patients, according to a study published Friday.

This higher in-hospital mortality rate — of 40% for COVID-19 patients versus 19% for influenza patients — was independent of patients’ age, gender, co-occurring health conditions, and severity of illness while in the ICU, according to the study published in the Annals of the American Thoracic Society.

The study is believed to be the first in the United States to directly compare clinical features, laboratory results and health outcomes between COVID-19 patients and flu patients.

Lead author Dr. Natalie Cobb, a pulmonary and critical care medicine physician with UW Medicine, and her co-authors reviewed the medical records of 65 patients critically ill with COVID-19 and 74 with severe influenza A or B who were admitted to the intensive care units of two UW Medicine hospitals between Jan. 1, 2019, and April 15, 2020.

The study found that COVID-19 patients had an in-hospital death rate of 40%, versus 19% for influenza patients and that they needed to remain on mechanical ventilation longer, had worse lung functioning and were more like to develop severe lung inflammation than were those with the flu.

“The finding that ARDS (acute respiratory distress syndrome) may be more prevalent among critically ill patients with COVID is important in understanding why there may be a mortality difference between the two diseases,” Cobb said. “We also found that patients with ARDS due to COVID-19 had a trend toward worse clinical outcomes than ARDS patients with influenza.”

The researchers noted that, early in the COVID outbreak, many comparisons were made between COVID-19 and infection with influenza, which is responsible for a significant number of hospitalizations and deaths, both in the United States and globally. While previous studies did not directly compare the two diseases, research has shown that important differences exist between the two diseases in the proportion of individuals with severe illness and mortality.

Said Cobb, “I strongly encourage people to get the flu vaccine and continue social-distancing measures and masking to limit the spread of COVID-19.”