We observed that Foxo1 and IL-9 expression is increased in active human Covid19 patients, and in the lungs of SARS-CoV-2-infected hamster and ACE2.Tg mice (Fig. 3a–d; Supplementary Fig. 7a), suggesting that Foxo1-IL-9 axis might be critical for SARS-CoV-2 infection and lung inflammation. Here, IL9 is linked to COVID-19.