Live virus neutralizing antibodies against pre and post Omicron strains in food and retail workers in Québec, Canada

Objectives To assess the neutralization activity pre and post Omicron BA.1 emergence in a unique cohort of 280 vaccinated restaurant/bar, grocery and hardware store workers in Québec, Canada. Methods Participants were recruited during the emergence of Omicron BA.1 variant. The neutralizing activity of participant sera was assessed by microneutralization assay. Results Serum neutralizing antibody (NtAb) titers of all participants against the ancestral SARS-CoV-2 strain was comparable with the response against Delta variant, however, their response was significantly reduced against Omicron BA.1, BA2, BA.2.12.1, BA.4 and BA.5. The neutralizing response of each group of workers was similar. Individuals who received 2 doses of vaccine had significantly reduced NtAb titers against all SARS-CoV-2 strains compared to those infected and then vaccinated (≥1 dose), vaccinated (≥2 doses) and then infected, or those who received 3 doses of vaccine. Participants vaccinated with 2 or 3 doses of vaccine and then infected had the highest NtAb titers against all SARS-CoV-2 strains tested. Conclusion We assessed for the first time the NtAb response in food and retail workers. Individuals infected after ≥2 doses of vaccine had the highest levels of NtAbs against Omicron BA.1, BA.2 and BA.5 variants and might be better protected against reinfection.