Antibody Response to Symptomatic Infection With SARS‐CoV‐2 Omicron Variant Viruses, December 2021–June 2022.

We describe humoral immune responses in 105 ambulatory patients with laboratory‐confirmed SARS‐CoV‐2 Omicron variant infection. In dried blood spot (DBS) collected within 5 days of illness onset and during convalescence, we measured binding antibody (bAb) against ancestral spike protein receptor binding domain (RBD) and nucleocapsid (N) protein using a commercial multiplex bead assay. Geometric mean bAb concentrations against RBD increased by a factor of 2.5 from 1258 to 3189 units/mL and by a factor of 47 against N protein from 5.5 to 259 units/mL between acute illness and convalescence; lower concentrations were associated with greater geometric mean ratios. Paired DBS specimens may be used to evaluate humoral response to SARS‐CoV‐2 infection. [ABSTRACT FROM AUTHOR]