Neutralization sensitivity of FL.1 and GE.1 from therapeutic antibodies and seropositive XBB sera

Two SARS-COV-2 XBB sub-variants, FL.1 and GE.1, have been increasing in prevalence worldwide, but limited information is available about their ability to evade the immune system. FL.1 and GE.1 possess additional mutations located in the spike RBD compared to XBB.1.5, raising concerns of increased neutralization escape. In this study, we assessed the neutralizing ability of eleven FDA-approved monoclonal antibody combinations against different omicron variants, including BA.2.75, BA.2.76, BA.4/5, XBB.1.5, and CH.1.1. Among the eleven antibodies, sotrovimab was the only antibody to show neutralization ability against XBB variants. However, sotrovimab showed broad but attenuated neutralization efficiency against XBB sub-lineages EG.5, FL.1, and GE.1 compared to XBB.1.5. Additionally, XBB.1.5 seropositive convalescent sera showed lower neutralization activity against EG.5, FL.1, and GE.1. Overall, our findings present enhanced immune evasion capacity of emerging XBB variants and emphasize the importance of continued monitoring of novel variants.