Evaluation of anti-SARS-CoV-2 S-RBD antibodies production and their persistence over time among a cohort of family clusters, including children and parents, after SARS-CoV-2 infection.

Background. While it is known that SARS-CoV-2 antibodies may persist in adults 12 months after the infection, there are few data on the pediatric population. We previously proved that children recovered from mild or asymptomatic COVID-19 present an intense early NAbs production: they were found to persist up to 7-8 months in children while adults recorded a modest declining trend. To date, the longer-term kinetics of Abs in children remains to be investigated. Objective. We herein describe the long-term anti-SARS-CoV-2 S-RBD IgG kinetics in children following SARS-CoV-2 infection. Methods. From April 2020 to August 2021, a single-center, prospective observational cohort study was conducted on 252 family clusters of COVID-19 evaluated consecutively at the COVID-19 Family Cluster Follow-up Clinic set up at the Department of Women's and Children's Health of the University Hospital of Padua. All patients with confirmed infection at enrolment underwent serological follow-up at 1-4, 5-10, and >10 months after infection with quantification of anti-SARS-CoV-2 S-RBD IgG by chemiluminescent immunoassay. Results. Among 902 study participants, 697 were confirmed COVID-19 cases, including 351 children/older siblings aged of 8.6±5.1years, and 346 parents with aged 42.5±7.1 years. Of those, 96.5% cases had asymptomatic/mild COVID-19. Children showed significantly higher S-RBD IgG titers than older patients across all follow-up time points, with an overall mean S-RBD IgG titer in patients < 3 years of age five-fold higher than adults (304.8 [139-516.6] kBAU/L vs 55.6 [24.2-136.0] kBAU/L, p<0.0001). The longitudinal analysis of 56 study participants sampled at least twice during follow-up demonstrated the persistence of antibodies up to 10 months from infection in all age classes, despite a progressive significant decline over time. Conclusion. In this study, we confirmed the different kinetics of the SARS-CoV-2 S-RBD IgG across several age classes of asymptomatic/mild COVID-19 cases. We proved that antibodies persisted until 12 months after infection in all age groups, with a significant peak Abs titer inversely related to age. Indeed, we found that the magnitude of SARS-CoV-2 S-RBD IgG Abs is higher among younger children than older siblings and adults at all follow-up time points.