ABSTRACT
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.
ABSTRACT
The COVID-19 pandemic is caused by the betacoronavirus SARS-CoV-2. In November 2021, the Omicron variant was discovered and classified as a variant of concern (VOC). Omicron shows substantially more mutations in the spike protein than any previous variant, mostly in the receptor binding domain (RBD). We analyzed the binding of the Omicron RBD to the human ACE2 receptor (hACE2) and the ability of human sera from COVID-19 patients or vaccinees in comparison to Wuhan, Beta or Delta RBDs variants. All RBDs were produced in insect cells. RBD binding to hACE2 was analyzed by ELISA and microscale thermophoresis (MST). Similarly, sera from 27 COVID-19 patients, 58 fully vaccinated individuals and 16 booster recipients were titrated by ELISA on the fixed RBDs from the original Wuhan strain, Beta, Delta and Omicron VOC. Surprisingly, the Omicron RBD showed a weaker binding to ACE2 compared to Beta and Delta, arguing that improved ACE2 binding is not a likely driver of Omicron evolution. Serum antibody titers were significantly lower against Omicron RBD compared to the original Wuhan strain. However, a difference of 2.5 times was observed in RBD binding while in other studies the neutralization of Omicron SARS-CoV-2 was reduced by a magnitude of 10x and more. These results indicate an immune escape focused on neutralizing antibodies. The reduced binding of sera to Omicron RBD adds evidence that current vaccination protocols may be less efficient against the Omicron variant.
