The emergence of the omicron and delta variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has begun a number of discussions regarding breakthrough infection, waning immunity, need and timing for vaccine boosters, and whether existing mRNA vaccines for the original SARS-CoV-2 strain are adequate. Our work leverages a biosensor-based technique to evaluate the binding efficacy of SARS-CoV-2 S1-specific salivary Abs to the omicron and delta variants using a cohort of mRNA-vaccinated (n = 109) and convalescent (n = 19) subjects. We discovered a wide range of binding efficacies to the variant strains, with a mean reduction of 60.5, 26.7, and 14.7% in measurable signal to the omicron strain and 13.4, 2.4, and -6.4% mean reduction to the delta variant for convalescent, Pfizer-, and Moderna-vaccinated groups, respectively. This assay may be an important tool in determining susceptibility to infection or need for booster immunization as the pandemic evolves.
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