L’émergence de la variante Omicron (B.1.1.529) du SRAS-CoV-2 avec des mutations majeures de la protéine de pointe a suscité des inquiétudes quant à la possibilité d’un échappement à la neutralisation et d’une percée des infections chez les sujets vaccinés et ceux précédemment infectés par le SRAS-CoV-2. Nous avons mesuré les anticorps de protection croisée contre les variants chez les travailleurs de la santé et les résidents de maisons de retraite à partir d’échantillons prélevés 1 à 2 mois après la (3e) dose de rappel.
The emergence of SARS-CoV-2 Omicron variant (B.1.1.529) with major spike protein mutations has raised concern over potential neutralization escape and breakthrough infections among vaccinated and previously SARS-CoV-2 infected subjects. We measured cross-protective antibodies against variants in health care workers (HCW, n = 20) and nursing home residents (n = 9) from samples collected 1–2 months following the booster (3rd) dose. We also assessed the antibody responses in subjects infected before the Omicron era (n = 38) with subsequent administration of a single mRNA vaccine dose. Following booster vaccination, HCWs had high IgG antibody concentrations to the spike protein and neutralizing antibodies (NAb) were detectable against all variants. IgG concentrations among the elderly remained lower, and some lacked NAbs against the Beta and Omicron variants. NAb titers were significantly reduced against Delta, Beta and Omicron compared to wild-type virus regardless of age. Vaccination induced high IgG concentrations and variable titers of cross-reactive NAbs in previously infected subjects, whereas NAb titers against Omicron were barely detectable 1 month post-infection. High IgG concentrations with cross-protective neutralizing activity were detected after three COVID-19 vaccine doses in HCWs. However, lower NAb titers seen in the frail elderly suggest inadequate protection against Omicron breakthrough infections, yet protection against severe COVID-19 is expected. Neutralizing antibodies against variants of concern were detected up to 2.5 months after the 3rd COVID-19 mRNA vaccination in adults, whereas some elderly subjects did not have neutralization capacity against Beta and Omicron variants at 1 month after 3rd dose. Single mRNA vaccine after SARS-CoV-2 infection induced comparable antibody levels. This article is protected by copyright. All rights reserved