SARS-CoV-2 Omicron Variant Infection of Individuals with High Titer Neutralizing Antibodies Post-3rd mRNA Vaccine Dose

Background: Vaccination with COVID-19 mRNA vaccines prevent hospitalization and severe disease caused by wildtype SARS-CoV-2 and several variants, and likely prevented infection when serum neutralizing antibody (NAb) titers were >1:160. Preventing infection limits viral replication resulting in mutation, which can lead to the emergence of additional variants. Methods: During a longitudinal study to evaluate durability of a three-dose mRNA vaccine regimen (2 primary doses and a booster) using a rapid test that semi-quantitatively measures NAbs, the Omicron variant emerged and quickly spread globally. We evaluated NAb levels measured prior to symptomatic breakthrough infection, in groups infected prior to and after the emergence of Omicron. Results: During the SARS-CoV-2 Delta variant wave, 93% of breakthrough infections in our study occurred when serum NAb titers were <1:80. In contrast, after the emergence of Omicron, study participants with high NAb titers that had received booster vaccine doses became symptomatically infected. NAb titers prior to infection were >1:640 in 64% of the Omicron-infected population, >1:320 (14%), and >1:160 (21%). Discussion: These results indicate that high titers of NAbs elicited by currently available mRNA vaccines do not protect against infection with the Omicron variant, and that mild to moderate symptomatic infections did occur in a vaccinated and boosted population, although did not require hospitalization.