Objectives: To estimate the prevalence of children and adolescents reporting persistent symptoms after SARS-CoV-2 infection.

Design: A random sample of children and adolescents participated with their family members to a serological survey including a blood drawing for detecting antibodies targeting the SARS-CoV-2 nucleocapsid (N) protein and a questionnaire on COVID-19-related symptoms experienced since the beginning of the pandemic.

Setting: The study took place in the canton of Geneva, Switzerland, between June and July 2021.

Participant: 660 children aged between 2 and 17 years old.

Primary and secondary outcome: The primary outcome was the persistence of symptoms beyond 4 weeks comparing seropositive and seronegative participants. The type of declared symptoms were also studied as well as associated risk factors.

Results: Among seropositive children, the sex-adjusted and age-adjusted prevalence of symptoms lasting longer than 2 weeks was 18.3%, compared with 11.1% among seronegatives (adjusted prevalence difference (ΔaPrev)=7.2%, 95% CI: 1.5% to 13.0%). Among adolescents aged 12-17 years, we estimated the prevalence of experiencing symptoms lasting over 4 weeks to be 4.4% (ΔaPrev,95% CI: -3.8% to 13.6%), whereas no seropositive child aged 2-11 reported symptoms of this duration. The most frequently declared symptoms were fatigue, headache and loss of smell.

Conclusions: We estimated the prevalence of experiencing persistent symptoms lasting over 4 weeks to be around 4% among adolescents, which represents a large absolute number, and should raise awareness and concern. We did not observe meaningful differences of persistent symptoms between seropositive and seronegative younger children, suggesting that they may be less affected than their older counterparts.