Diminished neutralization responses towards SARS-CoV-2 Omicron VoC after mRNA or vector-based COVID-19 vaccinations

SARS-CoV-2 variants accumulating immune escape mutations provide a significant risk to vaccine-induced protection. The novel variant of concern (VoC) Omicron (B.1.1.529) has the largest number of amino acid alterations in its Spike protein to date. Thus, it may efficiently escape recognition by neutralizing antibodies, allowing breakthrough infections in convalescent and vaccinated individuals. We analyzed neutralization activity of sera from individuals after vaccination with all mRNA-, vector- or heterologous immunization schemes currently available in Europe by in vitro neutralization assay at peak response towards SARS-CoV-2 B.1, Omicron, Beta and Delta pseudotypes and also provide longitudinal follow-up data from BNT162b2 vaccinees. All vaccines apart from Ad26.CoV2.S showed high levels of responder rates (93-100%) towards SARS-CoV-2 wild-type, but some reductions in neutralizing Beta and Delta VoC pseudotypes. The novel Omicron variant had the biggest impact, both in terms of response rates and neutralization titers. Only mRNA-1273 showed a 100% response rate to Omicron and induced the highest level of neutralizing antibody titers, followed by heterologous prime-boost approaches. Homologous BNT162b2 vaccination or vector-based AZD1222 or Ad26.CoV2.S performed less well with peak responder rates of 33%, 50% and 9%, respectively. However, Omicron responder rates in BNT162b2 recipients were maintained in our six month longitudinal follow-up indicating that individuals with cross-protection against Omicron maintain it over time. Overall, our data strongly argues for urgent booster doses in individuals who were previously vaccinated with BNT162b2, or a vector-based immunization scheme.