Publication date: May 30, 2024

Measuring the ability of SARS-CoV-2 antibodies to neutralize live viruses remains an effective approach to quantify the level of protection of individuals. We assessed the neutralization activity against the ancestral SARS-CoV-2, Delta, Omicron BA. 1, BA. 2, BA. 2.12. 1, BA. 4 and BA. 5 strains, in 280 vaccinated restaurant/bar, grocery and hardware store workers in QucE9bec, Canada. Participants were recruited during the emergence of Omicron BA. 1 variant. The neutralizing activity of participant sera was assessed by microneutralization assay. Serum neutralizing antibody (NtAb) titers of all participants against the ancestral SARS-CoV-2 strain were comparable with those against Delta variant (ranges of titers 10-2032 and 10-2560, respectively), however, their response was significantly reduced against Omicron BA. 1, BA2, BA. 2.12. 1, BA. 4 and BA. 5 (10-1016, 10-1016, 10-320, 10-80 and 10-254, respectively). 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. We assessed for the first time the NtAb response in food and retail workers. We found that vaccination prior to the emergence of Omicron BA. 1 was associated with higher neutralizing activity against pre-Omicron variants, suggesting the importance of updating vaccines to increase antibody response against new SARS-CoV-2 variants. Vaccination followed by infection was associated with higher neutralizing activity against all SARS-CoV-2 strains tested.

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