ACE2 and infection: In fact, a clinical analysis revealed that co-infection of SARS-CoV-2 and influenza virus resulted in more severe clinical symptoms and higher mortality rate than separate infections.32 Other results showed that influenza virus enhanced SARS-CoV-2 infection through promoting Angiotensin-converting enzyme 2 (ACE2) expression.33 However, the influence of SARS-CoV-2 on the infection of influenza virus remain unknown.