SARS-CoV-2 seroepidemiology in paediatric population during Delta and Omicron predominance

Abstract

Limited prospective severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) data in children regarding the impact of Omicron variant in seropositivity have been reported. We investigated SARS-CoV-2 seropositivity in children between 1 September 2021 and 30 April 2022, representing Delta and Omicron predominance periods. Serum samples from children admitted to the major tertiary Greek paediatric hospital for any cause, except for COVID-19, were randomly collected and tested for SARS-CoV-2 natural infection antibodies against nucleocapsid antigen (Elecsys® Anti-SARS-CoV-2 reagent). A total of 506/1312 (38.6%) seropositive children (0-16 years) were detected (males: 261/506(51.6%); median age (IQR): 95.2 months(24-144)). Seropositivity rates (%) increased from Delta to Omicron period from 29.7% to 48.5% (P-value<0.0001). Seropositivity increased for all age groups, except for the age group of 0-1 year (P-value:0.914). The highest seropositivity rate was detected in April 2022 (52.6%) and reached 73.9% specifically for the age group 12-16 years. No significant differences were detected in seropositivity with respect to gender, origin, or hospitalisation status. Median (IQR) antibody titres were higher in the Omicron vs. Delta period in all age groups, especially in 12-16 years [32.2 COI (7-77.1) vs. 11.4 COI(2.8-50.2), P-value:0.009). During Omicron variant period increased SARS-CoV-2 seropositivity was detected in paediatric population, especially in adolescents, implicating either increased transmissibility or reinfection rates.

Keywords: COVID-19; Children; Omicron variant; SARS-CoV-2; seroepidemiology.

Fig. 1.

Seropositivity (%) per month in 1312 children from September 2021 to April 2022 in Athens metropolitan area.

Fig. 2.

Seropositivity per month per age group from September 2021 to April 2022 in Athens metropolitan area.

Fig. 3.

Median antibody titres per age group in September 2021–December 2021 (Delta period) and January 2022–April 2022 (Omicron period) in Athens Metropolitan area. Lines represent median antibody titre values and bars represent interquartile range (IQR) values (COI, cut-off index).