Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection causes asymptomatic or mild symptoms, even rare hospitalization in children. A major concern is whether the pre-existing antibodies induced by low pathogenic human coronaviruses (LPH-CoVs) in children can cross-react with SARS-CoV-2. To address this unresolved question, we analyzed the pre-existing spike (S)-specific immunoglobin (Ig) G antibodies against LPH-CoVs and the cross-reactive antibodies against SARS-CoV-2 in 658 serum samples collected from children prior to SARS-CoV-2 outbreak. We found that the seroprevalence of these four LPH-CoVs reached 75.84%, and about 24.64% of the seropositive samples had cross-reactive IgG antibodies against the nucleocapsid, S, and receptor binding domain antigens of SARS-CoV-2. Additionally, the re-infections with different LPH-CoVs occurred frequently in children and tended to increase the cross-reactive antibodies against SARS-CoV-2. From the forty-nine serum samples with cross-reactive anti-S IgG antibodies against SARS-CoV-2, we found that seven samples with a median age of 1.4 years old had detected neutralizing activity for the wild-type or mutant SARS-CoV-2 S pseudotypes. Interestingly, all of the seven samples contained anti-S IgG antibodies against HCoV-OC43. Together, these data suggest that children’s pre-existing antibodies to LPH-CoVs have limited cross-reactive neutralizing antibodies against SRAS-CoV-2.

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The severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) pandemic is ongoing and multiple studies have elucidated its pathogenesis, however, the related‐ microbiome imbalance caused by SARS‐CoV‐2 is still not clear. In this study, we have comprehensively compared the microbiome composition and associated function alterations in the oropharyngeal swabs of healthy controls and coronavirus disease 2019 (COVID‐19) patients with moderate or severe symptoms by metatranscriptomic sequencing. We did observe a reduced microbiome alpha‐diversity but significant enrichment of opportunistic microorganisms in patients with COVID‐19 compared with healthy controls, and the microbial homeostasis was rebuilt following the recovery of COVID‐19 patients. Correspondingly, less functional genes in multiple biological processes and weakened metabolic pathways such as carbohydrate metabolism, energy metabolism were also observed in COVID‐19 patients. We only found higher relative abundance of limited genera such as Lachnoanaerobaculum between severe patients and moderate patients while no worthy‐noting microbiome diversity and function alteration were observed. Finally, we noticed that the co‐occurrence of antibiotic resistance and virulence was closely related to the microbiome alteration caused by SRAS‐CoV‐2. Overall, our findings demonstrate that microbial dysbiosis may enhance the pathogenesis of SARS‐CoV‐2 and the antibiotics treatment should be critically considered.