Escape of SARS-CoV-2 variant Omicron to mucosal immunity in vaccinated subjects

Omicron s escape to vaccine-induced systemic antibody responses has been shown in several studies in Omicron-infected patients and vaccine controls. In the present study we compared mucosal antibody response to Omicron to mucosal antibody response to ancestral strain and Delta variant. This was done on nasal epithelial lining fluid (NELF) prospectively collected in 84 otherwise healthy healthcare workers who had never exhibited PCR-documented COVID-19 and had received three doses of the Pfizer-BioNTech COVID-19 mRNA vaccine. NELF was collected prior to Omicron detection in the geographical area of inclusion. We show that NELF antibodies from vaccinated individuals were less efficient at inhibiting the binding of the Omicron Spike protein to ACE-2 compared to those of Delta or the ancestral strain. These findings may explain the increased risk of onward transmission of Omicron, consistent with its successful global displacement of Delta in countries with a high vaccination coverage.