Coronavirus disease 2019 (COVID-19) and influenza A outbreaks have spread rapidly in China. It is difficult to accurately differentiate these two different respiratory tract infections on the basis of their similar early-stage symptoms and lymphocytopenia. In the present study, the age, sex and white blood cell, neutrophil, lymphocyte, monocyte and eosinophil counts, as well as the neutrophil-to-lymphocyte ratio (NLR) of 201 outpatients with confirmed COVID-19 and 246 outpatients with influenza A were investigated and compared. A receiver operating characteristic curve was drawn to determine the thresholds in distinguishing COVID-19 from influenza A Our study found that the monocyte count and NLR were significantly elevated, while the eosinophil count/percentage was higher in outpatients with COVID-19 than in those with influenza A (0.06±0.07 vs. 0.04±0.09, P=0.002; 0.95±1.12 vs. 0.56±0.95, P<0.001, respectively). Logit(P)=-1.11 + 1.29 x eosinophil percentage -12.07 x eosinophil count +1.10 x monocyte count, deduced from the eosinophil count/percentage and monocyte count, had the largest area under the curve at 0.67, with high specificity (80.1%) and a sensitivity of 47.3%. The present study demonstrated that a higher eosinophil count/percentage may be a potential biomarker to significantly differentiate early COVID-19 from influenza A.