Study: Risk of death from COVID-19 is 3.5 times higher than from influenza

A new study published in CMAJ (Canadian Medical Association Journal) found that the risk of death from COVID-19 was 3.5 times higher than from influenza.

We can now say definitively that COVID-19 is much more severe than seasonal influenza. Patients admitted to hospital in Ontario with COVID-19 had a 3.5 times greater risk of death, 1.5 times greater use of the ICU, and 1.5 times longer hospital stays than patients admitted with influenza."

Dr. Amol Verma, St. Michael's Hospital, Unity Health Toronto,University of Toronto

These findings are similar to study results recently reported in France and the United States.

The study compared hospitalizations for influenza between November 1, 2019, and June 30, 2020, in 7 large hospitals in Toronto and Mississauga -- areas with large populations and high levels of COVID-19. It included all patients admitted to medical services or the intensive care unit (ICU) for influenza or COVID-19.

There were 783 hospitalizations for influenza in 763 unique patients compared with 1027 hospitalizations for COVID-19 in 972 unique patients (representing 23.5% of all hospitalizations for COVID-19 in Ontario during the study period).

Most patients hospitalized with COVID-19 had few other illnesses, and 21% were younger than 50 years of age. People younger than 50 also accounted for almost 1 in 4 (24%) admissions to the ICU.

"Many people believe that COVID-19 mainly affects older people," says Dr. Verma. "It is true that COVID-19 affects older adults most severely. We found that among adults over 75 years who were hospitalized with COVID-19, nearly 40% died in hospital. But it can also cause very serious illness in younger adults. Adults under 50 accounted for 20% of all COVID-19 hospitalizations in the first wave of the pandemic. Nearly 1 in 3 adults younger than 50 hospitalized with COVID-19 required intensive care, and nearly 1 in 10 required an unplanned readmission to hospital after discharge."

People hospitalized for COVID-19 had greater use of the ICU, were more likely to be put on a ventilator and had longer hospital stays than people with influenza.

"These differences may be magnified by low levels of immunity to the novel coronavirus compared with seasonal influenza, which results from past infections and vaccination," says Dr. Verma. "Hopefully, the severity of COVID-19 will decrease over time as people are vaccinated against the virus and more effective treatments are identified. There is, unfortunately, also the possibility that variants of the virus could be even more severe."