The continuing COVID-19 pandemic and emergence of SARS-CoV-2 variants may cause this disease to transit into endemicity like seasonal flu.In a recent study,Bai et al.reported that preinfection of influenza A virus enhanced SARS-CoV-2 infectivity,calling for the development of a pan-flu-COVID-19 vaccine to combat infection of IAV,SARS-CoV-2,or their coinfection.