摘要Coronavirus disease 2019(COVID-19)is rampant worldwide and has affected more than 215 countries and regions.According to the World Health Organization's report,there were 226,018,919 COVID-19 cases and 4,654,898 deaths as of March 14,2021,although 300,002,228 vaccines have been administered globally.COVID-19 patients have different clinical phenotypes and can be divided into asymptomatic,normal,mild,severe,and critical patients.However,the factors that lead to severe/critical cases remain controversial,and microecological dysfunction is one of the potential causes(Saleh et al.,2020).Previous studies have reported that the gut microbiome affects the severity of COVID-19(Zuo et al.,2020;Lv et al.,2021),but the correlations between the respiratory microbiome(RM)and COVID-19 severity have seldom been detected.Since the RM is closely related to the occurrence of COVID-19(Wypych et al.,2019),we propose to explore the RM characteristics in COVID-19 patients with different severities and elucidate the RM changes along with the clinical treatment.