Longitudinal survey of humoral and cellular response to SARS-CoV-2 infection in children.

Background: Data regarding humoral and cellular response against SARS-CoV-2 in children are scarce. We analysed seroconversion rate, decrease of anti-RBD IgG antibodies over time and T-cell response in paediatric patients who suffered COVID-19.

Methods: Longitudinal study of paediatric patients COVID-19 diagnosed by positive molecular assay in nasopharyngeal swabs. Blood samples were drawn 1-2 months and 6-7 months after acute infection. Anti-RBD IgG were determined using the Alinity® SARS-CoV-2 IgG II Quant assay (Abbott). Cellular immune response was analysed by T-SPOT® SARS-CoV-2 assay kit (Oxford Immunotec Ltd.).

Results: 27/39 (69,2%) patients seroconverted. Despite a significant decrease in antibody levels over time (p < 0,01), no children seroreverted between first and second visits. Only 6/16 (37,2%) children under 6 years-old were seropositive compared to 21/23 (91,3%) over 6 years-old (p < 0,01). Highest antibody levels were found in seropositive younger children (p = 0,036). Thirteen (33,3%) children showed T-cell response. Among participants showing humoral response, no cellular response was detected in 14 (51,9%).

Conclusions: Anti-RBD IgG antibodies persistence at 6-7-months after SARS-CoV-2 infection was observed. A different IgG response was found depending on age. As measured by T-SPOT, most patients did not display cellular response 6-7 months after infection.