Analysis of risk factors for long COVID after mild COVID-19 during the Omicron wave in Japan

Post-COVID-19 syndrome, referred to as "long COVID," is characterized by persistent symptoms that develop during or after SRAS-CoV-2 infection lasting for ≥12 weeks, which cannot be explained by factors other than COVID-19. Previous studies before the Omicron pandemic have identified female sex, older age (≥50 years), severity of illness, obesity, diabetes, and smoking as risk factors for long COVID. However, data on long COVID following the emergence of the Omicron variants are limited.

An online survey was conducted among outpatients diagnosed with mild COVID-19 at 14 participating institutions in Japan between July 30, 2022, and December 31, 2023.

Of the included 246 cases, 76 (35.5%) experienced at least one long COVID symptom 12 weeks after onset. Logistic regression analysis revealed that age ≥40 years was significantly associated with an increased risk of respiratory (odds ratio [OR]: 3.80, 95% confidence interval [CI]: 1.67-8.65) and neurologic symptoms (OR: 4.53, 95% CI: 1.84-11.13). Conversely, antiviral drug use was associated with a decreased risk of respiratory symptoms (OR: 0.31, 95% CI: 0.11-0.93).

Caution is warranted when treating patients over 40 years of age with mild COVID-19 due to their higher susceptibility to developing long COVID. Antiviral drugs may be beneficial in managing respiratory symptoms and mitigating disease severity.