Fig. 3.

Nasal and plasma antibody responses to variants of concern 12 months after infection. Nasal IgA (A–C), nasal IgG (D–G) and plasma IgG (G–I) responses to RBD of ancestral SARS-CoV-2, Delta, and Omicron (BA.1) variants in 446 COVID-19 patients compared to 25 pre-pandemic control samples (grey). Nasal virus-specific antibody titres were normalised to total IgA or IgG concentration. The horizontal dashed line indicates the threshold for positivity determined by the mean+2SD of controls. ∗ = p < 0.05, ∗∗ = p < 0.01, ∗∗∗ = p < 0.001, ∗∗∗∗ = p < 0.0001.