Objective:Traditional Chinese medicine plays a significant role in the treatment of the pandemic of coro-navirus disease 2019(COVID-19).Tanreqing Capsule(TRQC)was used in the treatment of COVID-19 patients in the Shanghai Public Health Clinical Center.This study aimed to investigate the clinical efficacy of TRQC in the treatment of COVID-19.Methods:A retrospective cohort study was conducted on 82 patients who had laboratory-confirmed mild and moderate COVID-19;patients were treated with TRQC in one designated hospital.The treatment and control groups consisted of 25 and 57 cases,respectively.The treatment group was given TRQC orally three times a day,three pills each time,in addition to conventional Western medicine treatments which were also administered to the control group.The clinical efficacy indicators,such as the negative conver-sion time of pharyngeal swab nucleic acid,the negative conversion time of fecal nucleic acid,the duration of negative conversion of pharyngeal-fecal nucleic acid,and the improvement in the level of immune indicators such as T-cell subsets(CD3,CD4 and CD45)were monitored.Results:COVID-19 patients in the treatment group,compared to the control group,had a shorter negative conversion time of fecal nucleic acid(4 vs.9 days,P = 0.047)and a shorter interval of negative conversion of pharyngeal-fecal nucleic acid(0 vs.2 days,P = 0.042).The level of CD3+T cells increased in the treat-ment group compared to the control group([317.09 ± 274.39]vs.[175.02 ± 239.95]counts/μL,P = 0.030).No statistically significant differences were detected in the median improvement in levels of CD4+T cells(173 vs.107 counts/μL,P= 0.208)and CD45+Tcells(366 vs.141 counts/μL,P = 0.117)between the treat-ment and control groups.Conclusion:Significant reductions in the negative conversion time of fecal nucleic acid and the duration of negative conversion of pharyngeal-fecal nucleic acid were identified in the treatment group as com-pared to the control group,illustrating the potential therapeutic benefits of using TRQC as a complement to conventional medicine in patients with mild and moderate COVID-19.The underlying mechanism may be related to the improved levels of the immune indicator CD3+T cells.