Omicron Infection Induces Low-Level, Narrow-Range SARS-CoV-2 Neutralizing Activity

Background The rapid worldwide spread of the mildly pathogenic SARS-CoV-2 Omicron variant has led to the suggestion that it will induce levels of collective immunity that will help putting an end to the COVID19 pandemics. Methods Convalescent serums from non-hospitalized individuals previously infected with Alpha, Delta or Omicron BA.1 SARS-CoV-2 or subjected to a full mRNA vaccine regimen were evaluated for their ability to neutralize a broad panel of SARS-CoV-2 variants. Findings Prior vaccination or infection with the Alpha or to a lesser extent Delta strains conferred robust neutralizing titers against most variants, albeit more weakly against Beta and even more Omicron. In contrast, Omicron convalescent serums only displayed low level of neutralization activity against the cognate virus and were unable to neutralize other SARS-CoV-2 variants. Interpretation Moderately symptomatic Omicron infection is only poorly immunogenic and does not represent a substitute for vaccination.Funding: EPFL COVID Fund; private foundation advised by CARIGEST SA; Private Foundation of the Geneva University Hospitals; General Directorate of Health of the canton of Geneva.Declaration of Interest: None to declare. Ethical Approval: The Geneva Cantonal Commission for Research Ethics approved this study (Project ID 2020-00881).