Safety, Tolerability, and Immunogenicity of VAX-31 in Adults ≥50 Years With Immunobridging to Adults 18-49

Inclusion Criteria: * Male or female ≥18 years of age (inclusive) at the time of randomization into the study. * Able and willing to complete the informed consent process. * Available for clinical follow-up through the last study visit. * In good general health or with stable underlying chronic condition(s), as determined by medical history, oral temperature, physical examination, and clinical judgment of the Investigator (ongoing chronic conditions must be documented as stable per Investigator). * Willing to have blood samples collected and used for research purposes. * Able to provide proof of identity to the satisfaction of the site personnel completing the enrollment process. * Female participants of childbearing potential, defined as premenopausal females capable of becoming pregnant, must have a negative urine pregnancy test immediately prior to randomization and agree to use acceptable contraception. Male subjects with partners of childbearing potential must agree to practice an acceptable contraception method. * Able to access and use a device connected to Wi-Fi or cellular network for completion of an electronic diary (eDiary). Exclusion Criteria: * History of invasive pneumococcal disease (IPD) or pneumococcal pneumonia (either confirmed or self-reported) at any age. * Previous receipt of any licensed or investigational pneumococcal vaccine at any age. * Receipt of any investigational product within 30 days prior to Day 1, currently participating in another inter…