Risk factors for post‐coronavirus disease condition in the Alpha‐, Delta‐, and Omicron‐dominant waves among adults in Japan: A population‐based matched case‐control study

Vaccination is associated with a reduced risk of post-coronavirus disease (COVID-19) condition (PCC). Here, risk factors including vaccination for PCC in the Omicron-dominant waves among Japanese adults were investigated. This was a registry-based matched case-control study of individuals aged 18-79 years diagnosed with COVID-19 registered in a National database between March 2021 and April 2022 and matched noninfected individuals living in Yao City, Japan. A self-administered questionnaire was used to assess persistent symptoms and their risk factors. The COVID-19 vaccination status was obtained from the Vaccination Registry. PCC risk factors were analyzed using logistic regression after adjusting for potential confounding factors. Overall, 4185 infected (cases) and 3382 noninfected (controls) individuals were included in the analysis. The mean ages and proportions of women were 44.7 years and 60.2% and 45.5 years and 60.7% for cases and controls, respectively. A total of 3805 (90.9%) participants had asymptomatic or mild acute symptoms at the median (range) follow-up of 271 (185-605) days. The prevalence of PCC was 15.0% for cases while that of persistent symptoms was 4.4% for controls; among the cases, it was 27.0% in the Alpha- and Delta-dominant waves and 12.8% in the Omicron-dominant wave. Female sex, comorbidities, and hospitalization were positively associated with PCC. One or more vaccine doses of vaccination were inversely associated with PCC; the inverse association was stronger in the Alpha- and Delta-dominant waves (adjusted odds ratio [aOR]: 0.29, 95% confidence interval [CI]: 0.12-0.73) than in the Omicron-dominant wave (aOR: 0.79, 95% CI: 0.59-1.07).