Clinical characteristics of critically ill patients co-infected with SARS-CoV-2 and the influenza virus in Wuhan, China

•A high proportion of COVID-19 patients were co-infected with influenza in Tongji Hospital (Wuhan).•Critically ill COVID-19 patients with influenza were more prone to cardiac injury than those without influenza.•Co-infection with the influenza virus may induce an earlier and more frequently occurring cytokine storm in critically ill COVID-19 patients.•Do not ignore detection of the influenza virus in patients with COVID-19.