Background:Coronavirus disease 2019(COVID-19)is pandemic.It is critical to identify COVID-19 patients who are most likely to develop a severe disease.This study was designed to determine the clinical and epidemiological features of COVID-19 patients associated with the development of pneumonia and factors associated with disease progression.rnMethods:Seventy consecutive patients with etiologically confirmed COVID-19 admitted to PLA General Hospital in Beijing,China from December 27,2019 to March 12,2020 were enrolled in this study and followed-up to March 16,2020.Differences in clinical and laboratory findings between COVID-19 patients with pneumonia and those without were determined by they2 test or the Fisher exact test(categorical variables)and independent group ttest or Mann-Whitney U test(continuous variables).The Cox proportional hazard model and Generalized Estimating Equations were applied to evaluate factors that predicted the progression of COVID-19.rnResults:The mean incubation was 8.67(95％confidence interval,6.78-10.56)days.Mean duration from the first test severe acute respiratory syndrome coronavirus 2-positive to conversion was 11.38(9.86-12.90)days.Compared to pneumonia-free patients,pneumonia patients were 16.5 years older and had higher frequencies of having hyperten-sion,fever,and cough and higher circulating levels of neutrophil proportion,interleukin-6,low count(＜ 190/μl)of CD8+T cells,and neutrophil/lymphocyte ratio.Thirteen patients deteriorated during hospitalization.Cox regression analysis indicated that older age and higher serum levels of interleukin-6,C-reactive protein,procalcitonin,and lactate at admission significantly predicted the progression of COVID-19.During hospitalization,circulating counts of T lymphocytes,CD4+T cells,and CD8+T cells were lower,whereas neutrophil proportion,neutrophil/lymphocyte ratio,and the circulating levels of interleukin-6,C-reactive protein,and procalcitonin were higher,in pneumonia patients than in pneumonia-free patients.CD8+lymphocyte count in pneumonia patients did not recover when discharged.rnConclusions:Older age and higher levels of C-reactive protein,procalcitionin,interleukin-6,and lactate might pre-dict COVID-19 progression.T lymphocyte,especially CD8+cell-mediated immunity is critical in recovery of COVID-19.This study may help in predicting disease progression and designing immunotherapy for COVID-19.