Long term antibody response to SARS-CoV-2 in children

ABSTRACT

Almost two years into the pandemic and with vaccination of children significantly lagging behind adults, long-term pediatric humoral immune responses to SARS-CoV-2 are understudied. The C19.CHILD Hamburg (COVID-19 Child Health Investigation of Latent Disease) Study is a prospective cohort study designed to identify and follow up children and their household contacts infected in the early 2020 first wave of SARS-CoV-2. We screened 6113 children <18 years by nasopharyngeal swab-PCR in a low-incidence setting after general lockdown, from May 11 to June 30, 2020. 4657 participants underwent antibody testing. Positive tests were followed up by repeated PCR and serological testing of all household contacts over 6 months. In total, the study identified 67 seropositive children (1.44 %), the median time after infection at first presentation was 83 days post-symptom onset (PSO). Follow up of household contacts showed incomplete seroconversion in most families, with higher seroconversion rates in families with adult index cases compared to pediatric index cases (OR 1.79, P=0.047). Most importantly, children showed sustained seroconversion up to nine months PSO, and serum antibody concentrations persistently surpassed adult levels (ratio serum IgG Spike children vs. adults 90 days PSO 1.75, P<0.001, 180 days 1.38, P=0.01, 270 days 1.54, P=0.001). In a low-incidence setting, SARS-CoV-2 infection and humoral immune response present distinct patterns in children including higher antibody levels, and lower seroconversion rates in families with pediatric index cases. Children show long-term SARS-CoV-2 antibody responses. These findings are relevant to novel variants with increased disease burden in children, as well as for the planning of age-appropriate vaccination strategies.