Antibody binding and ACE2 binding inhibition is significantly reduced for the Omicron variant compared to all other variants of concern

The rapid emergence of the Omicron variant and its large number of mutations has led to its classification as a variant of concern (VOC) by the WHO(1). Initial studies on the neutralizing response towards this variant within convalescent and vaccinated individuals have identified substantial reductions(2-8). However many of these sample sets used in these studies were either small, uniform in nature, or were compared only to wild-type (WT) or, at most, a few other VOC. Here, we assessed IgG binding, (Angiotensin-Converting Enzyme 2) ACE2 binding inhibition, and antibody binding dynamics for the omicron variant compared to all other VOC and variants of interest (VOI)(9), in a large cohort of infected, vaccinated, and infected and then vaccinated individuals. While omicron was capable of binding to ACE2 efficiently, antibodies elicited by infection or immunization showed reduced IgG binding and ACE2 binding inhibition compared to WT and all VOC. Among vaccinated samples, antibody binding responses towards omicron were only improved following administration of a third dose. Overall, our results identify that omicron can still bind ACE2 while pre-existing antibodies can bind omicron. The extent of the mutations appear to inhibit the development of a neutralizing response, and as a result, omicron remains capable of evading immune control.

Reduced serum neutralization capacity against SARS-CoV-2 variants in a multiplex ACE2 RBD competition assay

As global vaccination campaigns against SARS-CoV-2 proceed, there is particular interest in the longevity of immune protection, especially with regard to increasingly infectious virus variants. Neutralizing antibodies (Nabs) targeting the receptor binding domain (RBD) of SARS-CoV-2 are promising correlates of protective immunity and have been successfully used for prevention and therapy. As SARS-CoV-2 variants of concern (VOCs) are known to affect binding to the ACE2 receptor and by extension neutralizing activity, we developed a bead-based multiplex ACE2-RBD inhibition assay (RBDCoV-ACE2) as a highly scalable, time-, cost-, and material-saving alternative to infectious live-virus neutralization tests. By mimicking the interaction between ACE2 and the RBD, this serological multiplex assay allows the simultaneous analysis of ACE2 binding inhibition to the RBDs of all SARS-CoV-2 VOCs and variants of interest (VOIs) in a single well. Following validation against a classical virus neutralization test and comparison of performance against a commercially available assay, we analyzed 266 serum samples from 168 COVID-19 patients of varying severity. ACE2 binding inhibition was reduced for ten out of eleven variants examined compared to wild-type, especially for those displaying the E484K mutation such as VOCs beta and gamma. ACE2 binding inhibition, while highly individualistic, positively correlated with IgG levels. ACE2 binding inhibition also correlated with disease severity up to WHO grade 7, after which it reduced.