A Clinical Study to Evaluate the Safety, Tolerability, and Immunogenicity of VAX-31 With Influenza Vaccine in Adults ≥ 50 Years of Age

Inclusion Criteria: 1. Male or female ≥50 years of age (inclusive) at the time of randomization into the study. 2. Able and willing to complete the informed consent process. 3. Available for clinical follow-up through the last study visit at 7 months after the first study vaccination. 4. 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. 5. Willing to have blood samples collected and used for research purposes. 6. Able to provide proof of identity to the satisfaction of the study site personnel completing the enrollment process. 7. Female subjects of childbearing potential, defined as premenopausal females capable of becoming pregnant, must have a negative urine pregnancy test at Screening and immediately prior to each vaccination and agree to use acceptable contraception, if heterosexually active. Female subjects who are not abstinent from heterosexual intercourse must agree to consistently practice contraception at least 7 days prior to vaccination and through their last study visit. Male subjects with partners of childbearing potential must agree to practice an acceptable contraception method (\[use condoms with or without spermicide\] or have undergone a vasectomy) from Day 1 through their last study visit. Note: A history of amenorrhea for at least 12 months without an alternative medical cause is required for a female to be considered postmenopausal in the study. 8. Able to access and use a device connected to Wi-Fi or cellular network for completion of an electronic diary (eDiary). Exclusion Criteria: 1. History of IPD or pneumococcal pneumonia (either confirmed or self-reported) at any age. 2. Previous receipt of a licensed or investigational pneumococcal vaccine at any age. 3. Previous receipt of an influenza vaccine from the current season; receipt of any influenza vaccine (licensed or investigational) within 6 months prior to Day 1; or receipt/planned receipt of any licensed or investigational non-study influenza vaccine during study participation. 4. Receipt of any investigational product within 30 days prior to Day 1, currently participating in another interventional investigational study, or having plans to receive another investigational product(s) while on study. 5. Planned or actual administration of any licensed vaccine within 30 days prior to Day 1. 6. Body temperature \>38.0°C (\>100.4°F) or acute illness within 3 days prior to study vaccination (participant may be rescreened). 7. Current diagnosis of human immunodeficiency virus (HIV), Hepatitis B, or Hepatitis C. 8. History of severe allergic reaction with generalized urticaria, angioedema, or anaphylaxis to any previous vaccination. 9. History of Guillain-Barré syndrome. 10. Individual who is pregnant, breastfeeding, or planning to become pregnant during study participation. 11. Has a known or suspected immunocompromising condition, including, but not limited to, leukemia, lymphoma, chronic renal failure, or congenital or acquired immunodeficiency. 12. Bleeding disorder diagnosed by a doctor (e.g., factor deficiency, coagulopathy, or platelet disorder requiring special precautions) resulting in clinically significant bruising or bleeding difficulties with IM injections or blood draws. 13. Receipt of blood or blood product (including polyclonal intravenous immunoglobulin) within 60 days prior to Day 1. 14. Receiving immunosuppressive therapy. 15. Received any part of a ≥14-day course of systemic corticosteroids (prednisone equivalent \>10 mg/day) within 14 days of study vaccinations. Note: Receipt of a ≥14-day course of systemic corticosteroids equivalent to ≤10 mg/day is permitted, as are inhaled, nebulized, topical, intra-articular, and intrabursal corticosteroids. 16. History of malignancy ≤5 years before to Day 1, except for adequately treated basal cell or squamous cell skin cancer or in situ cervical cancer. 17. Any medical, psychiatric, or social condition that in the judgment of the Investigator is a contraindication to protocol participation or impairs a participant's ability to give informed consent. 18. Employee of, or first-degree relative of any person employed by the Sponsor, the contract research organization (CRO), the Investigator, study site personnel, or site.