Prevalence of and Risk Factors for Post-COVID-19 Condition during Omicron BA.5-Dominant Wave, Japan

Abstract

The increased risk for post-COVID-19 condition after the Omicron-dominant wave remains unclear. This population-based study included 25,911 persons in Japan 20-69 years of age with confirmed SARS-CoV-2 infection enrolled in the established registry system during July-August 2022 and 25,911 age- and sex-matched noninfected controls who used a self-reported questionnaire in January-February 2023. We compared prevalence and age- and sex-adjusted odds ratios of persistent COVID-19 symptoms (lasting ≥2 months). We evaluated factors associated with post-COVID-19 condition by comparing cases with and without post-COVID-19 condition. We analyzed 14,710 (8,392 cases and 6,318 controls) of 18,183 respondents. Post-COVID-19 condition proportion among cases was 11.8%, higher by 6.3% than 5.5% persistent symptoms among controls. Female sex, underlying medical conditions, mild to moderate acute COVID-19, and vaccination were associated with post-COVID-19 condition. Approximately 12% had post-COVID-19 condition during the Omicron-dominant wave, indicating the need for longer follow-up.

Keywords: BA.5; COVID-19; Japan; Omicron; SARS-CoV-2; post–COVID-19 condition; post–acute COVID-19 syndrome; prevalence; respiratory infections; risk factors; severe acute respiratory syndrome coronavirus 2; viruses; zoonoses.

Figure 1

Flowchart of participant selection in study of prevalence and risk factors for post–COVID-19 condition during Omicron BA.5–dominant wave, Japan. Of 29,276 residents 20–69 years of age identified in the municipal HER-SYS database as infected with COVID-19, we selected a total of 25,911 participants; we extracted the same number of age- and sex-matched noninfected residents from the Basic Residence Registration System to serve as the control group. HER-SYS, Health Center Real-time Information-sharing System on COVID-19.

Figure 2

Prevalence and age- and sex-adjusted odds ratios of persistent symptoms in cases compared with controls in study of prevalence and risk factors for post–COVID-19 conditions during Omicron BA.5–dominant wave, Japan. All cases and controls are included in the multivariable logistic regression analysis to estimate the odds ratio of developing post–COVID-19 condition among cases compared with controls adjusting for age (as a continuous variable) and sex.