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.