Neutralization activity of IgG antibody in COVID‑19‑convalescent plasma against SARS-CoV-2 variants

Abstract Coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). We evaluated the anti-SARS-CoV-2 antibody levels, anti-spike (S)-immunoglobulin G (IgG) and anti-nucleocapsid (N)-IgG, and the neutralization activity of IgG antibody in COVID‑19‑convalescent plasma against variants of SARS-CoV-2, alpha, beta, gamma, delta, kappa, omicron and R.1 strains. The study included 30 patients with clinically diagnosed COVID-19. The anti-S-IgG and anti-N-IgG levels ranged from 30.0 to 555.1 and from 10.1 to 752.6, respectively. The neutralization activity (50% inhibition concentration: IC50) for the wild-type Wuhan strain ranged from 100 µg/ml in 18 of 30 (60%) subjects infected with the beta variant. The IC50 values for wild-type and beta variants correlated inversely with anti-S-IgG levels (p