Antibodies to SARS-CoV-2 were tested in children aged 1 to 18 years living in Bavaria, Germany, participating in a public health type 1 diabetes screening program, the Fr1da study.
Antibodies testing was performed in capillary blood using LIPS assays. A dual-positive antibody response against both the receptor binding domain (RBD) and the nucleocapsid protein (NP) of SARS-CoV-2 was interpreted as ‘recovered from infection/exposure to SARS-CoV-2’ or ‘recovered and vaccinated’; a positive antibody response against the receptor binding domain with titers above 5000 BAU and a negative response against the nucleocapsid protein of SARS-CoV-2 was interpreted as ‘vaccinated against SARS-CoV-2 without prior infection’.
Children with positive responses against the receptor binding domain with titers below 5000 BAU and a negative response against the nucleocapsid protein of SARS-CoV-2 are interpreted as an ‘early response to vaccination or infection/exposure’ or a ‘waning response to a much earlier previous infection/exposure’.