Myth: It’s Just a Flu

[This was one of the first myths I tried to debunk in early March, 2020, when my website was just a blog.]

Differences in clinical characteristics and outcomes between COVID-19 and influenza in critically ill adult patients: A national database study (2023)

Patients with COVID-19 were less likely to receive invasive mechanical ventilation but had a higher likelihood of in-hospital death. Whether or not they received invasive mechanical ventilation, mortality was consistently higher in patients with COVID-19 than in patients with influenza, especially among those who were 65 years and older and independently of the invasive mechanical ventilation status.

Despite the lower rate of organ support, we found that COVID-19 was strongly associated with a higher likelihood of in-hospital death after adjustment for age, gender, comorbidities, and severity at ICU admission.

Comparison of patient characteristics and in-hospital mortality between patients with COVID-19 in 2020 and those with influenza in 2017–2020: a multicenter, retrospective cohort study in Japan (2022)

Our results were largely compatible with those of previous studies from Europe or North America regarding the higher mortality and the longer hospital stay among patients with COVID-19 than those with influenza. Differences in the risks of death between COVID-19 and influenza might be partly explained by the fact that effective vaccination and appropriate treatments are available for influenza, but not for COVID-19, at least by the end of 2020 in Japan. It should also be noted that, in line with previous studies the number of patients with influenza in 2020 was one-half to one-third of that between 2017–2019, probably because the prevention measures for COVID-19, such as mask and physical distancing, were effective in preventing influenza infection.

As for the supportive care, the necessity of mechanical ventilation, ECMO, and renal replacement therapy did not differ between COVID-19 and influenza patients on the admission day, but COVID-19 patients were more likely to require these treatments during the entire hospitalisation period. Patients with COVID-19 tended to experience a deterioration of their condition after hospitalisation compared to those with influenza, which seemingly led to a higher risk of in-hospital death. Notably, when mechanical ventilation was started, the in-hospital mortality (both crude and adjusted) did not differ between the study groups.

Comparison of clinical characteristics and disease outcome of COVID-19 and seasonal influenza (2021)

Even though COVID-19 patients were generally younger and healthier than influenza patients, the overall course of disease was more severe, with fewer patients treated as outpatients, longer overall duration of hospitalization, more frequent admission to the ICU, more frequent need for oxygen therapy, and invasive ventilation.

Comparison of Critical Care Occupancy and Outcomes of Critically Ill Patients during the 2020 COVID-19 Winter Surge and 2009 H1N1 Influenza Pandemic in Australia (2021)

Comparative evaluation of clinical manifestations and risk of death in patients admitted to hospital with covid-19 and seasonal influenza: cohort study (2020)

Our results suggest that compared with seasonal influenza, covid-19 was associated with higher risk of acute kidney injury, incident renal replacement therapy, incident insulin use, severe septic shock, vasopressor use, pulmonary embolism, deep venous thrombosis, stroke, acute myocarditis, arrythmias and sudden cardiac death, elevated troponin, elevated aspartate aminotransferase, elevated alanine aminotransferase, and rhabdomyolysis. Covid-19 was also associated with increased risk of death, need for mechanical ventilation, and admission to ICU and prolonged length of hospital stay.

Comparison of the characteristics, morbidity, and mortality of COVID-19 and seasonal influenza: a nationwide, population-based retrospective cohort study (2020)