SeroCovid19 : prospective seroprevalence monitoring reveals substantially reduced SARS-CoV-2 infection rate among tertiary pediatric patients

Background Coronavirus disease 2019 (COVID-19) is a clinically heterogeneous entity with several host, environmental, and viral risk factors identified to date. COVID-19 in children generally manifests asymptomatic or mild. Pediatric patients with chronic medical conditions are potentially at increased risk for severe COVID-19, although convincing data is lacking. Among these children, we aimed to study COVID-19 incidence and disease severity. Methods We initiated a prospective cohort study with longitudinal (every 3-6 months) quantification of serum SARS-CoV-2 IgG (Abbott) and questionnaires in pediatric patients (0-18y) with chronic medical conditions in follow-up at Ghent University Hospital, a tertiary referral center. This interim analysis incorporates inclusions from Nov 1, 2020 until Jan 14, 2021. Results Here, we present data of the first 250 included patients (mean age 10.4y). Chronic conditions required follow-up at departments of immunology (26.4%), nephrology (16.7%), rheumatology (15.4%), gastroenterology (14.5%), endocrinology (8.8%), pulmonology (8.8%) or others (9.3%). Chronic immunosuppressive drugs were used in 35.6%. Inborn errors of immunity, possibly affecting antibody responses, were present in 18.0%. Restriction from school or daycare centers (additional to general lockdown and school closures) was documented in 35.1% and 10.7%, before and after the summer break, respectively. Since the start of the pandemic, close contacts with proven COVID-19 were known in 21.0%. An overall SARS-CoV-2 seroprevalence of 6.0% (15/250) was found, substantially lower than concurrently reported in Belgian blood donors and health care workers (14.4% in Nov 2020), and on the lower end compared to healthy children measured prior to the second epidemic wave in Flanders (4.4-14.4% in Sept-Oct). Asymptomatic COVID-19 was documented in 7/15. One patient with cystic fibrosis (9y) required hospitalization. All other cases experienced mild COVID-19, at most. Of seropositive cases, 5/15 received immunosuppression, all experiencing mild infection. Conclusion A strikingly low SARS-CoV-2 seroprevalence was found in our cohort. Despite no supplementary preventive measures were imposed for the majority, this cohort seemed additionally shielded from SARS-CoV-2. Asymptomatic COVID-19 was present in half of cases. These findings may be of importance for ongoing and future protective measures, clinical management, and vaccination strategies in these population