Fig. 6.

Distinct gut and respiratory microbiome mechanisms associated with the progress of COVID-19 in adults and children. The dynamic mechanism of the microbiome in adults was interpreted from our recent observation based on the longitudinal throat and anal swabs from 35 adults with COVID-19 (Xu et al., 2021). Similar community types from I to III/IV indicate a progressive dysbiosis of the microbiome. In mild adults with COVID-19, a synchronous shift of community type from early dysbiosis towards late incomplete restoration was found in both respiratory and gut microbiomes within a short time. In children, however, the changes of the community types were divergent between the respiratory tract and gut, possibly implying that the “airway-gut axis” is still not established during the childhood. Moreover, children's respiratory microbiome appeared to be progressively deteriorating for a long period despite a fast clinical recovery. RV, respiratory virus.