ImportanceThe prevalence and baseline risk factors of post–COVID-19 condition (PCC) remain unresolved among the large number of young people who experienced mild COVID-19.ObjectivesTo determine the point prevalence of PCC 6 months after the acute infection, to determine the risk of development of PCC adjusted for possible confounders, and to explore a broad range of potential risk factors.Design, Setting, and ParticipantsThis cohort study included nonhospitalized individuals from 2 counties in Norway between ages 12 and 25 years who underwent reverse transcription–polymerase chain reaction (RT-PCR) testing. At the early convalescent stage and at 6-month follow-up, participants underwent a clinical examination; pulmonary, cardiac, and cognitive functional testing; immunological and organ injury biomarker analyses; and completion of a questionnaire. Participants were classified according to the World Health Organization case definition of PCC at follow-up. Association analyses of 78 potential risk factors were performed.ExposuresSARS-CoV-2 infection.Main Outcomes and MeasuresThe point prevalence of PCC 6 months after RT-PCR testing in the SARS-CoV-2–positive and SARS-CoV-2–negative groups, and the risk difference with corresponding 95% CIs.ResultsA total of 404 individuals testing positive for SARS-CoV-2 and 105 individuals testing negative were enrolled (194 male [38.1%]; 102 non-European [20.0%] ethnicity). A total of 22 of the SARS-CoV-2–positive and 4 of the SARS-CoV-2–negative individuals were lost to follow-up, and 16 SARS-CoV-2–negative individuals were excluded due to SARS-CoV-2 infection in the observational period. Hence, 382 SARS-CoV-2–positive participants (mean [SD] age, 18.0 [3.7] years; 152 male [39.8%]) and 85 SARS-CoV-2–negative participants (mean [SD] age, 17.7 [3.2] years; 31 male [36.5%]) could be evaluated. The point prevalence of PCC at 6 months was 48.5% in the SARS-CoV-2–positive group and 47.1% in the control group (risk difference, 1.5%; 95% CI, −10.2% to 13.1%). SARS-CoV-2 positivity was not associated with the development of PCC (relative risk [RR], 1.06; 95% CI, 0.83 to 1.37; final multivariable model utilizing modified Poisson regression). The main risk factor for PCC was symptom severity at baseline (RR, 1.41; 95% CI, 1.27-1.56). Low physical activity (RR, 0.96; 95% CI, 0.92-1.00) and loneliness (RR, 1.01; 95% CI, 1.00-1.02) were also associated, while biological markers were not. Symptom severity correlated with personality traits.Conclusions and RelevanceThe persistent symptoms and disability that characterize PCC are associated with factors other than SARS-CoV-2 infection, including psychosocial factors. This finding raises questions about the utility of the World Health Organization case definition and has implications for the planning of health care services as well as for further research on PCC.

The prevalence and predictors of long COVID in young people remain unresolved. We aimed to determine the point prevalence of long COVID in non-hospitalised adolescents and young adults six months after the acute infection, to determine the risk of developing long COVID adjusted for possible confounders, and to explore a broad range of potential risk factors (prespecified outcomes). We conducted a prospective controlled cohort study of 404 SARS-CoV-2-positive and 105 SARS-CoV-2-negative non-hospitalised individuals aged 12–25 years (ClinicalTrial ID: NCT04686734). Data acquisition was completed February 2022. Assessments included pulmonary, cardiac and cognitive functional testing, biomarker analyses, and completion of a questionnaire, and were performed at inclusion (early convalescent stage) and six months follow-up. The WHO case definition of long COVID was applied. The point prevalence of long COVID at six months was 49% and 47% in the SARS-CoV-2-positive and negative group, respectively. SARS-CoV-2-positivity did not predict development of long COVID (relative risk 1.06, 95% CI 0.83 to 1.37). The main predictor was symptom severity at inclusion, which correlated strongly to personality traits. Low physical activity and loneliness were also predictive, while biological markers were not. In conlusion, our study aims were met, and the findings suggest that persistent symptoms were not driven by the infection, but were associated with psychosocial factors.