Age dependent discrepancy between SARS-CoV-2 anti-nucleoprotein antibody and anti-RBD spike protein antibody in children reflects vaccine coverage

Abstract

BackgroundCOVID-19 has become widespread in Japanese children. However, the impact of varying immunization coverage on the seroprevalence of SARS-CoV-2 in children is unknown. MethodsWe examined the SARS-CoV-2 antibody in children aged 0 to 18 who were hospitalized at a university hospital from June 2020 through May 2023. The SARS-CoV-2 anti-nucleoprotein (N) antibody and anti-RBD spike (S) protein antibody was measured. ResultsA total of 586 cases were enrolled. The median age was 4 years old (interquartile range 1–9), and 362 (61.8 %) were male. The seroprevalence of anti-S antibodies gradually increased from October 2021 and reached 60 percent by early 2023. The anti-N antibody increased starting in January 2022 and reached 50 percent in May 2023. There was a discrepancy in the seroprevalence of anti-S and N antibodies in children 0 years of age or 12 years and older until the fall of 2022. This discrepancy was minimal for children 1–4 years of age and relatively small in the 5–11-year-old group. DiscussionThe data suggests that approximately half of the children in our cohort had been infected with SARS-CoV-2 by May 2023. The discrepancy in seropositivity between the anti-S and N antibodies corresponded to the reported vaccine uptake of each target age group, which suggested protective effects of immunization. However, this effect appeared to diminish after early 2023. ConclusionAge dependent discrepancy between SARS-CoV-2 anti-N and anti-S antibody in children reflected differences in vaccine coverage.