This is a summary, written by members of the CITF Secretariat, of

Rabezanahary H, Gilbert C, Santerre K, Scarrone M, Gilbert M, Theriault M, Brousseau N, Masson J-M, Pelletier JN, Boudreau D, Trottier S, Baz M. Live virus neutralizing antibodies against pre and post Omicron strains in food and retail workers in Quebec, Canada. medRxiv. doi:

The results and/or conclusions contained in the research do not necessarily reflect the views of all CITF members.

A CITF-funded study, published in preprint and not yet peer-reviewed, found that vaccination was associated with higher neutralizing activity (the ability of antibodies to block entry of the virus into the cell) against pre-Omicron variants than against Omicron sub-lineages. Vaccination followed by infection was associated with higher neutralizing activity against Omicron sub-lineages than vaccination alone. Interestingly, there was no significant difference in the neutralizing response in terms of sex, age, chronic diseases, and whether food and retail workers smoked or vaped. This study was led by Dr. Denis Boudreau (Université Laval).

Key findings:

  • Among study participants, neutralizing antibody (NtAb) levels in the blood were similar against the ancestral SARS-CoV-2 strain and the Delta variant. However, neutralizing responses were significantly reduced against Omicron BA.1, BA2, BA.2.12.1, BA.4, and BA.5. This was true for each group of participating workers (grocery stores, hardware stores, and restaurants/bars).
  • Individuals who received two vaccine doses had significantly reduced NtAb titers against all SARS-CoV-2 strains, compared to those infected and then vaccinated with one or more doses, those vaccinated with two or more doses and then infected, or those who received three doses of vaccine.
  • Participants vaccinated with two or three doses of vaccine who were then infected had the highest NtAb titers against all SARS-CoV-2 strains tested. There was no significant difference in participants’ neutralizing responses in terms of sex, age, chronic disease, and whether they smoked or vaped.

This study highlights the importance of up-to-date vaccination for food and retail workers to stimulate an effective neutralizing response against Omicron variants.

Blood samples were collected from 380 vaccinated participants, who were recruited from a longitudinal study of food and retail workers (individuals who work in grocery stores, restaurants/bars, or hardware stores) in the Québec City area (Capitale-Nationale and Chaudière-Appalaches regions) from October 2021 to May 2022, during the emergence of the Omicron BA.1 variant. There were two age groups: those under 60 years and those 60 years and older.