Fig. 4

Diversity differences in the oral microbiome and specific microbiomes with significantly increased relative abundance in follow-up patient saliva samples. A Rarefaction analysis showed that as the number of saliva samples increased, the number of nonredundant genes approached saturation in the mild (n = 45), follow-up (n = 45), and normal (n = 25) groups. B The Shannon index of the oral microbiome in the follow-up group. C The Jaccard distance between the different groups reflects the low similarity of microbial composition in saliva samples from the follow-up group to the normal group and mild COVID-19 patients. D The NMDS based on the relevant abundance of the microbiome in the follow-up group, normal, and mild groups. E,F Average relative abundance of the top five phyla (E) and top 10 microbial genera (F) detected in saliva from normal individuals, in-hospital patients, and their follow-up within 3 months after discharge. G,H The microbial phyla (G) and top 10 genera (H) with significantly higher relative abundance in fecal samples from 3-month follow-up patients compared with normal samples or in-hospital patients I. Average relative abundance of top 79 microbial species detected in oral microbiota from the Normal, Mild, and Follow-up samples. J The KEGG functions that were significantly enhanced or reduced in the follow-up group. K The top 20 microbial species with significantly high relative abundance in saliva samples of follow-up patients compared to normal samples or mild patients. “ns” represents no significance, *p < 0.05, ** p < 0.01, ##p < 0.01, ***p < 0.001, and ****p < 0.0001 (Student’s t test)