Immunogenic relationship mapping supports a minimal-set trivalent vaccine strategy for broad sarbecovirus protection

Major outbreaks of severe acute respiratory syndrome (SARS) and coronavirus disease 2019 (COVID-19), together with the continuous risk of zoonotic spillover of animal sarbecoviruses, underscore the urgent need for vaccines that confer broad protection across the sarbecovirus subgenus. Current immunogen selection strategies for pansarbecovirus vaccine development predominantly rely on phylogenetic or spike sequence conservation analyses, which often fail to accurately predict the breadth of cross-neutralization. To overcome this limitation, we systematically evaluated cross-neutralization profiles among 25 representative sarbecoviruses from clades 1 and 3 via guinea pig antisera individually raised against full-length spike proteins in pseudovirus neutralization assays while excluding clade 2 viruses lacking known receptor usage. Neutralization profiling revealed four distinct immunogenic clusters that diverged from traditional phylogenetic relationships. Antisera induced by the palm civet-derived SARS-CoV-1 strain SZ1 broadly neutralized all clade 1a viruses, whereas full coverage of clade 1b viruses required at least two distinct immunogens. Remarkably, sera elicited by multiple clade 1 immunogens also neutralized clade 3 viruses despite no prior exposure to clade 3 antigens. Guided by these findings, we proposed a minimal trivalent immunogen combination-SZ1, SARS-CoV-2, and PCoV-GX-that elicited broad neutralization against both clade 1 and clade 3. This rational approach eliminates the need for additional clade 3-specific antigens and provides a preclinical framework for developing next-generation pansarbecovirus vaccines.