A Single Chimeric Spike Antigen Induces Pan-Sarbecovirus Immunity

Next-generation vaccines are required to address the evolving nature of SARS-CoV-2 and to protect against emerging pandemic threats from other coronaviruses. These vaccines should aim to elicit broad-protection, provide long-lasting immunity and facilitate equitable access for all populations. In this study, a panel of chimeric, full-length spike antigens were developed that incorporate mutations from previous, circulating and predicted SARS-CoV-2 variants. The lead candidate (CoVEXS5) was obtained from a high-yield production process in stable CHO cells with purity of >95%, long-term stability and elicitation of broadly cross-reactive neutralising antibodies when delivered to mice in a squalene emulsion adjuvant (Sepivac SWE). In both mice and hamsters, CoVEXS5 immunisation reduced clinical disease signs, lung inflammation and organ viral titres after SARS-CoV-2 infection, including challenge with the highly immunoevasive Omicron XBB.1.5 subvariant. In mice previously primed with a licenced protein vaccine (NVX-CoV2373), CoVEXS5 could boost T cell immunity, as well as neutralising antibodies levels against viruses from three sarbecoviruses clades. The breadth of sarbecovirus cross-reactivity elicited by CoVEXS5 exceeded that observed after boosting with the NVX-CoV2373 vaccine. These findings highlight the potential of a chimeric spike antigen, formulated in an open-access adjuvant, as a next-generation vaccine candidate to enhance cross-protection against emerging sarbecoviruses in vaccinated populations globally.