Background Children are discussed as hidden SARS‐CoV‐2 virus reservoir because of predominantly mild or even asymptomatic course of disease. The objective of this cross‐sectional study in May‐July 2020 was to assess the prevalence of SARS‐CoV‐2 antibodies and virus RNA in schoolchildren, consistent with previous infection by contact tracing. Methods School authorities approached parents for voluntary participation. Interested families were contacted by the study team. A nasal and oropharyngeal swab, a blood sample, and a questionnaire were employed. Primary endpoint was the frequency of SARS‐CoV‐2 real‐time PCR (RT‐PCR) and antibody‐positive children. Antibody positivity was assessed by a highly sensitive first‐line ELISA, and a neutralization assay and two other immunoassays as confirmatory assays. Results Of 2069 children (median age 13 years, IQR 10‐15), 2 cases (0.1%) tested positive for SARS‐CoV‐2 RNA and 26 cases (1.3%) tested positive for specific antibodies. SARS‐CoV‐2‐specific antibodies exhibited detectable virus‐neutralizing activity in 92% (24 of 26 samples). Seropositivity was associated with a history of mild clinical symptoms in 14 children (53.8%), while 12 children (46.2%) remained asymptomatic. Among 13 seropositive children being tested concomitantly with their siblings, only one pair of siblings was seropositive. Contact tracing revealed adult family members and school teachers as potential index cases. Conclusion In schoolchildren, the infection rate with SARS‐CoV‐2 is low and associated with a mild or asymptomatic course of disease. Virus spreading seemed to occur more likely in intergenerational contacts than among siblings in the same household. The presence of neutralizing SARS‐CoV‐2 antibodies in children may reflect protective adaptive immunity.

SARS-CoV-2 infection is effectively controlled by humoral and cellular immune responses. However, the durability of immunity in children as well as the ability to neutralize variants of concern are unclear. Here, we assessed T cell and antibody responses in a longitudinal cohort of children after asymptomatic or mild COVID-19 over a 12-month period. Antigen-specific CD4 T cells remained stable over time, while CD8 T cells declined. SARS-CoV-2 infection induced long-lived neutralizing antibodies against ancestral SARS-CoV-2 (D614G isolate), but with poor cross-neutralization of omicron. Importantly, recall responses to vaccination in children with pre-existing immunity yielded neutralizing antibody activities against D614G and omicron BA.1 and BA.2 variants that were 3.9-fold, 9.9-fold and 14-fold higher than primary vaccine responses in seronegative children. Together, our findings demonstrate that SARS-CoV-2 infection in children induces robust memory T cells and antibodies that persist for more than 12 months, but lack neutralizing activity against omicron. Vaccination of pre-immune children, however, substantially improves the omicron-neutralizing capacity.

Background While children usually experience a mild course of COVID‐19, and a severe disease is more common in adults, the features, specificities, and functionality of the SARS‐CoV‐2‐specific antibody response in the pediatric population are of interest. Methods We performed a detailed analysis of IgG antibodies specific for SARS‐CoV‐2‐derived antigens S and RBD by ELISA in 26 SARS‐CoV‐2 seropositive schoolchildren with mild or asymptomatic disease course, and in an equally sized, age‐ and gender‐matched control group. Furthermore, a detailed mapping of IgG reactivity to a panel of microarrayed SARS‐CoV‐2 proteins and S‐derived peptides was performed by microarray technology. The capacity of the antibody response to block RBD‐ACE2 binding and virus neutralization were assessed. Results were compared with those obtained in an adult COVID‐19 convalescent population. Results After mild COVID‐19, anti‐S and RBD‐specific IgG antibodies were developed by 100% and 84.6% of pediatric subjects, respectively. No difference was observed in regards to symptoms and gender. Mounted antibodies recognized conformational epitopes of the spike protein and were capable to neutralize the virus up to a titer of ≥80 and to inhibit the ACE2‐RBD interaction by up to 65%. SARS‐CoV‐2‐specific IgG responses in children were comparable to mildly affected adult patients. Conclusion SARS‐CoV‐2 asymptomatic and mildly affected pediatric patients develop a SARS‐CoV‐2‐specific antibody response, which is comparable regarding antigen, epitope recognition, and the ability to inhibit the RBD‐ACE2 interaction to that observed in adult patients after mild COVID‐19.