Long-term symptoms after SARS-CoV-2 infection in school children: population-based cohort with 6-months follow-up

Although long COVID in children exists, it is still unclear to what extent children are affected. The Ciao Corona study is a longitudinal cohort investigating SARS-CoV-2 seroprevalence and clustering of cases among around 2500 children and adolescents (hereafter referred to as children) from 55 randomly selected primary and secondary schools in the canton of Zurich in Switzerland. Between June 2020 and April 2021, we completed three testing phases where we collected venous blood for serological analysis and asked about symptoms with online questionnaires. We compared children who tested positive for SARS-CoV-2 antibodies in October/November 2020 with those who tested negative. Children who were seronegative in October/November 2020 and seroconverted or were not retested in March/April 2021 were excluded from the analysis (n=256). In March-May 2021 we assessed the presence of symptoms occurring since October 2020, lasting for at least 4 weeks, and persisting for either >4 weeks or >12 weeks. Overall, 1355 of 2503 children with a serology result in October/November 2020 and follow up questionnaire in March-May 2021 were included. Among seropositive and seronegative 6-to 16-year-old children, 9% versus 10% reported at least one symptom beyond 4 weeks, and 4% versus 2% at least one symptom beyond 12 weeks. None of the seropositive children reported hospitalization after October 2020. This study suggests a low prevalence of symptoms compatible with long COVID in a randomly selected population-based cohort of children followed over 6 months after serological testing.