Emergence and antibody evasion of BQ, BA.2.75 and SARS-CoV-2 recombinant sublineages in the face of maturing antibody breadth at the population level
Authors: Akerman Anouschka , Milogiannakis Vanessa , Jean Tyra , Esneau Camille , Silva Mariana Ruiz , Ison Timothy , Fitcher Christina , Lopez Joseph A , Chandra Deborah , Naing Zin , Caguicla Joanna , Li Daiyang , Walker Gregory , Amatayakul-Chantler Supavadee , Roth Nathan , Manni Sandro , Hauser Thomas , Barnes Thomas , Condylios Anna , Yeang Malinna , Wong Maureen , Foster Charles S.P. , Sato Kenta , Lee Sharon , Song Yang , Mao Lijun , Sigmund Allison , Phu Amy , Vande More Ann Marie , Hunt Stephanie , Douglas Mark , Caterson Ian , Sandgren Kerrie , Bull Rowena , Lloyd Andrew , Triccas Jamie , Tangye Stuart , Bartlett Nathan W , Darley David , Matthews Gail , Stark Damien J. , Rawlinson William D. , Murrell Ben , Brilot Fabienne , Cunningham Anthony L , Kelleher Anthony D. , Aggarwal Anupriya , Turville Stuart G. 
Published: December 2022

The Omicron era of the COVID-19 pandemic commenced at the beginning of 2022 and whilst it started with primarily BA.1, it was latter dominated by BA.2 and related sub-lineages. Over the course of 2022, we monitored the potency and breadth of antibody neutralization responses to many emerging variants at two levels: (i) we tracked over 420,000 U.S. plasma donors over time through various vaccine booster roll outs and Omicron waves using sequentially collected IgG pools; (ii) we mapped the antibody response in individuals using blood from strigently curated vaccine and convalescent cohorts. In pooled IgG samples, we observed the maturation of neutralization breadth to Omicron variants over time through continuing vaccine and infection waves. Importantly, in many cases we observed increased antibody breadth to variants that were yet to be in circulation. Determination of viral neutralization at the cohort level supported equivalent coverage across prior and emerging variants with emerging isolates BQ.1.1, XBB.1, BR.2.1 and XBF the most evasive. Further, these emerging variants were resistant to Evusheld, whilst neutralization resistance to Sotrovimab was restricted to BQ.1.1 and XBF. We conclude at this current point in time that dominant variants can evade antibodies at levels equivalent to their most evasive lineage counterparts but sustain an entry phenotype that continues to promote an additional outgrowth advantage. In Australia, BR2.1 and XBF share this phenotype and are dominating across NSW and Victoria.

Research in context

Evidence before this study

Up until the BA.5 wave in mid 2022, many global waves were seeded by dominant variants such as Delta, Omicron BA.1 and Omicron BA.2. Following resolution of the BA.5, was the emergence of a pool of BA.4/5 and BA.2.75 sub-lineages accumulating clusters of similar polymorphisms located with the Receptor Binding Domain (RBD) of the Spike glycoprotein. Although iterative changes in the Spike increased the ability of each variant to navigate existing neutralising antibodies, it was unclear if this alone was sufficient to provide an outgrowth advantage to any one variant to fuel major case waves in global communities with high vaccine uptake and/or infection.

Added value of this study

Prior studies on incoming variants in Australian quarantine, highlighted the potential for Australia to represent a unique mix of cocirculating variants. Following the resolution of the BA.5 Omicron wave, many globally circulating variants appeared early on and ranged from BA.2.75 lineages, recombinants XBB.1, and XBC.1 in addition to many BA.5 derived BQ.1 lineages. Two additional lineages, the recombinant XBF and the BA.2.75 derived BR.2.1 also appeared and were uniquely enriched in Australia. Using 14 primary clinical isolates covering a continuum of circulating variants in Australia, we resolved neutralisation responses of 110 donors stringently documented for their vaccine and infection status over time. In addition, we also tested the well clinical utilised clinical monoclonals Evusheld and Sotrovimab. In addition to tracking donors, we also tracked immunity at the population level, using pooled IgG samples over time. The latter samples were the sum of 420,000 US plasma donors covering time periods of high-booster uptake alongside and in addition to large case waves. Whilst the above resolved the impact of Spike changes in neutralisations, we also tested each variant with respect to the efficiency of TMPRSS2 use, as this significantly influences viral tropism across the respiratory tract.

Implications of all the available evidence

All variants analysed herein have undertaken a convergent trajectory in accumulating a similar cluster of Spike polymorphisms. Many variants, including BQ.1.1, XBB.1, XBF and BR.2.1 have accumulated key changes that now render neutralisation responses lower in all cohorts and are neutralisation resistant to Evusheld. Whilst sotrovimab retained neutralisation capacity of many variants, there was significant reduction for variants BQ.1.1 and XBF. Impact of Spike changes on TMPRSS2 use were mixed and only one variant, BQ.1.2, had equal to increased usage relative to its parent BA.5. Analysis of neutralisation at the population level over time revealed two key observations. Firstly, whilst variants converged and lowered neutralisation responses, this reduction was negated over time with increasing neutralisation breadth. Secondly, responses to a variant proceeded its appearance and global circulation. In conclusion, whilst many variants are appearing and iterative changes in the spike will challenge antibody responses, increasing breadth in the community over time has enabled sufficient coverage to presently emerging variants. Furthermore, with the exception of BQ.1.2, viral use of TMPRSS2 has not increased and as such viral tropism towards epithelial cells of the upper respiratory tract we predict will be maintained.