Background. The objective of this study was to investigate the difference in disease severity between influenza A and B among hospitalized adults using a novel ordinal scale and existing clinical outcome end points. Methods. A prospective, observational study was conducted over the 2016-2018 influenza seasons in a central hospital. The primary outcome was the rate of clinical improvement, defined as a decline of 2 categories from admission on a 7-category ordinal scale that ranges from 1 (discharged with normal activity) to 7 (death), or hospital discharge up to day 28. Results. In total, 574 eligible patients were enrolled, including 369 (64.3%) influenza A cases and 205 (35.7%) influenza B cases. The proportion of patients with a worse ordinal scale at admission was higher in influenza A than influenza B (P = .0005). Clinical improvement up to 28 days occurred in 82.4% of patients with influenza A and 90.7% of patients with influenza B (P = .0067). The Cox model indicated that influenza B patients had a higher clinical improvement probability than influenza A cases (adjusted hazard ratio [HR], 1.266; 95% confidence interval [CI], 1.019-1.573; P = .0335). A similar pattern was observed in weaning oxygen supplement (adjusted HR, 1.285; 95% CI, 1.030-1.603; P = .0261). In-hospital mortality for influenza A was marginally higher than influenza B (11.4% vs 6.8%; P = .0782). Conclusions. Our findings indicated that hospitalized patients with influenza A were more ill and had delayed clinical improvement compared with those with influenza B virus infection.