Safety, Tolerability, and Immunogenicity of VAX-31 in Adults ≥50 Years With Prior Pneumococcal Vaccination

Inclusion Criteria: * Male or female ≥50 years of age (inclusive) at the time of randomization into the study. * Previous receipt of a licensed pneumococcal vaccine or combination of licensed vaccines, with most recent vaccination ≥1 year prior to randomization; the exception is PCV21, which may have been received ≥6 months prior to randomization (confirmed). * 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: * Previous invasive pneumococcal disease (IPD) or pneumococcal pneumoni…