APECx is an ARPA-H program focused on improving vaccine-antigen discovery for broader protection against viral families. It supports work in high-throughput biochemical analysis and protein engineering, protein-modeling tools for antigen design, and translational candidate development and clinical evaluation. The program’s approach combines computational modeling with experimental analysis to design antigens, then evaluates candidate antigens to assess the tools’ accuracy. ARPA-H describes the intended outcome as toolkits that could help develop broadly effective vaccines against multiple virus threats.