Streptococcus pyogenes or Group A Streptococcus (GAS) is a major cause of non-invasive and invasive infections resulting in an estimated 500,000 deaths annually. Vaccination would reduce GAS morbidity and mortality but is challenging due to serotype diversity, general antigenic variation, and vaccine safety concerns related to autoimmune sequelae. The Group A Carbohydrate (GAC) is universally expressed by all GAS serotypes. For decades, the GAC was thought to be structurally uniform and conserved, consisting of a polyrhamnose backbone with alternating N-acetylglucosamine (GlcNAc) side chains. As such, the GAC has been instrumental for clinical rapid diagnostics and is included in preclinical vaccine studies due to its universal and seemingly invariable expression within the GAS population. Recently, we discovered that ~30% of the GAC GlcNAc side chains carry a glycerol phosphate (GroP) modification, adding a new feature to the GAS pathogenesis and vaccine landscape. This presentation will highlight how different GAC glycoforms affect immune recognition and bacterial virulence. First, GroP modifications of the GAC affect susceptibility to human antimicrobial proteins and zinc toxicity. Second, we have developed a bead-based multiplex assay using chemically-synthesized well-defined glycan fragments to assess i) how the presence of the GroP modification impacts opsonization by GAC-(vaccine) induced antibodies, ii) the natural immunogenicity of the three GAC glycoforms using human plasma in healthy controls and patients with invasive GAS disease, and iii) generate monoclonal and polyclonal antibodies towards the three distinct GAC glycoforms to study their protective capacity in in vitro and in vivo assays. Overall, this work spans the entire spectrum from molecule to organism to patients with the aim to advance the development of a GAC-based vaccine to prevent GAS infections.