Abstract
Limited prospective serosurveillance data in children regarding severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection have been reported. We prospectively investigated SARS-CoV-2 seropositivity in children during a 16-month period of the coronavirus disease 2019 (COVID-19) pandemic, including the four waves of the pandemic, before SARS-CoV-2 adolescents' vaccination. Serum samples from children admitted to the major tertiary Greek pediatric hospital for any cause, except for COVID-19 infection, were randomly collected from 05/2020 to 08/2021. The study period was divided into four 4-month periods representing relevant epidemic waves. Total SARS-CoV-2 antibodies for nucleocapsid protein were determined using the Elecsys® Anti-SARS-CoV-2 reagent. A total of 3099 children (0-16 years) were included in the study. A total of 344 (11.1%) seropositive children were detected (males: 205 [59.5%]; median age [interquartile range [IQR]]: 3 years [0.6-10]). Seropositivity rates (%) increased during the four 4-month periods: 1.4%, 8.6%, 17.2%, and 17.6%, respectively. A correlation of seropositivity rates in children with new diagnosed SARS-CoV-2 cases in the community was detected. No significant differences were detected between males and females. Seropositivity was significantly higher in hospitalized than in nonhospitalized children and in non-Greek compared to Greek children (p < 0.001). The lowest seropositivity rate before school opening (9/2021) was detected in the age groups 6-12 years (14.4%) and 12-16 years (16.1%). However, compared with the other age groups, the lowest median antibody titers were observed in children 0-1 year (median [IQR]: 13.9 cut-off index: [4.5-53.9] [p < 0.001]). Although the seropositivity of children was related to the community epidemic waves, the exposure was limited. Low seropositivity rates in school-age children support the need for SARS-CoV-2 immunization.