The SARS-CoV-2 Omicron variant of concern1 (VOC) is highly resistant to vaccine-induced antibody neutralization2 and associated with a decline in vaccine efficacy within the first 3 months following the primary 2-dose regimen of the SARS-CoV-2 BNT162b2 (Pfizer/BioNTech) mRNA vaccine3,4 and from 10 weeks after a third BNT162b2 dose.4
To associate Omicron-specific neutralizing antibody levels with reported vaccine efficacies, we performed a temporal analysis of virus neutralization responses against an ancestral strain (D614G), the Delta VOC, and the Omicron VOC (BA.1) following 2 or 3 doses of the BNT162b2 vaccine.
This cohort study includes Danish adults who received 2 or 3 doses of BNT162b2 between January 2021 and October 2021 or were previously infected prior to February 2021 and then vaccinated. In the latter group, given the timeframe, individuals became infected with ancestral SARS-CoV-2 strains before VOCs became dominant in Denmark. We determined 50% serum neutralization titers using a live virus microneutralization assay5 (eAppendix in the Supplement).