Frequency and Duration of the Clinical Symptoms of Patients With Mild COVID‐19: A Comparison With Influenza in the 2023–2024 Japanese Influenza Season, an Observational Study

Background and Aims This study aimed to compare the clinical symptoms of mild COVID‐19 and influenza during a period when both diseases circulated in the 2023–2024 influenza season in Japan. Methods Outpatients diagnosed with COVID‐19, influenza A, or influenza B by antigen test kits at 10 medical facilities in Japan were enrolled. Data were collected from a self‐reported diary. Results Data from 347 COVID‐19, 392 influenza A, and 103 influenza B patients were analyzed. COVID‐19 patients were significantly older than those with influenza A and B ( p < 0.001). Sore throat was significantly more prevalent in COVID‐19 patients than in patients with influenza A or B (49.0% vs. 27.3% and 27.2%, p < 0.001). Cough and nasal discharge/congestion were significantly more common in influenza A and B patients than in COVID‐19 patients ( p < 0.001 and p < 0.001, respectively). Taste and smell dysfunction at Days 5 to 7 was more prevalent in COVID‐19 patients (6.9% and 6.9%, respectively) than in influenza A or B patients ( p < 0.001 and p < 0.001, respectively). Maximum body temperature was significantly lower in COVID‐19 patients than in influenza A or B patients (38.3°C vs. 38.9°C and 38.9°C, p < 0.001). The frequency of any symptoms over 14 days was significantly higher in COVID‐19 patients, particularly in those aged ≥ 40 years ( p < 0.001). Conclusion Mild COVID‐19 was associated with longer‐lasting symptoms than influenza, particularly in individuals aged ≥ 40 years. These results suggest a greater disease burden of COVID‐19, even in outpatients with mild disease, compared with influenza.