Age and prior vaccination determine the antibody level in children with primary SARS-CoV-2 Omicron infection

Background: Protection against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) reinfection relies on immunity generated after primary infection. However, humoral immunity following primary infection with the Omicron variant is not well understood. Methods: We prospectively recruited children <19 years with virologically-confirmed SARS2022 during the first wave of Omicron BA.2 outbreak in Taiwan. Serum samples were collected one month after acute infection to measure anti-spike protein receptor binding domain antibody levels and surrogate virus neutralizing antibody (NAb) levels against wild type disease and variants.Results: Of the 164 patients enrolled, most were under 5 years (65.2%) with a diagnosis of up-per respiratory tract infection. Children under 6 months with maternal coronavirus disease 2019 (COVID-19) vaccination had higher levels of both anti-SARS-CoV-2 spike antibody (119.0 vs 27.4 U/ml, p < 0.05) and anti-wild type NAb (56.9% vs 27.6% inhibition, p Z 0.001) than those without. Children aged 5-12 years with prior vaccination had higher anti-spike antibody, anti-wild type, and anti-Omicron BA.2 NAb levels than those without (all p < 0.05). In previ-ously naive children without maternal or self-vaccination, those 6 months to 2 years had the highest antibody levels. Multivariable linear regression analysis showed age was the only inde-pendent factor associated with antibody level.Conclusions: In our study, children aged 6 months to 2 years have the highest antibody re-sponses to SARS-CoV-2 Omicron variant infection. Age and prior vaccination are the main fac-tors influencing the immunogenicity of SARS-CoV-2 infection.Copyright 2023, Taiwan Society of Microbiology. Published by Elsevier Taiwan LLC. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).