Study to Evaluate a 25-Valent Pneumococcal Conjugate Vaccine

• Healthy adults who are 18 through 40 years old on the day of randomization (Day 1).
• Subject, or subject's LAR, must provide voluntary written informed consent for the subject to participate in the study.
• Subject or subject's LAR must be able to comprehend and comply with study requirements and procedures and must be willing and able to return for all scheduled follow-up visits.
• There will be an allowance though not a requirement for COVID-19 vaccination in all participants in compliance with Canadian national recommendations.
• Adult female subjects who are not surgically sterile must have a negative serum pregnancy test at screening and negative urine pregnancy test prior to vaccination.

Exclusion Criteria:

• Use of any investigational medicinal product within 90 days prior to randomization or planned use of such a product during the period of study participation.
• Adults who have previously been vaccinated against S. pneumoniae.
• History of microbiologically confirmed invasive disease caused by S. pneumoniae.
• History of allergic disease or history of a serious reaction to any prior vaccination or known hypersensitivity to any component of the study vaccines.
• Known or suspected allergy to PEG.
• History of angioedema.
• Any abnormal vital sign deemed clinically relevant by the PI.
• Acute illness (moderate or severe) and/or fever (body temperature of ≥ 38.0°C)
• Use of antibiotics (oral or parenteral) within 5 days of randomization.
• History of administration of any non-study vaccine (e.g. influenza; COVID-19 vaccine) within 14 days of first administration of study vaccine or planned vaccination prior to 14 days post-vaccination blood draw.
• Chronic administration (defined as more than 14 consecutive days) of immunosuppressant or other immune modifying drugs prior to the administration of the study vaccine (and within the 6 months prior to administration of the study vaccine in the case of adults), including the use of glucocorticoids. The use of topical and inhaled glucocorticoids will be permitted.
• Administration of immunoglobulins and/or any blood products within the 6 months prior to administration of the study vaccine, or anticipation of such administration during the study period.
• History of known disturbance of coagulation or blood disorder that could cause anemia or excess bleeding (e.g., thalassemia, coagulation factor deficiencies, severe anemia).
• Any medical or social condition that in the opinion of the PI , may interfere with the study objectives, pose a risk to the subject, or prevent the subject from completing the study follow-up.
• Subject is an employee of, or direct descendant (child or grandchild) of any person employed by the Sponsor, PATH, the CRO, the PI.
• Any screening laboratory test result outside the normal range and with toxicity score ≥ 2, unless allowed by the PI and PATH Medical Officer when a toxicity score and the normal range overlap significantly. A subject may repeat each laboratory assessment once during the screening period, with the most recent laboratory value being used for evaluation of exclusion criteria.
• A positive serologic test for human immunodeficiency virus (HIV)-1 or HIV-2 (HIV 1/2 Ab), hepatitis B (HBsAg) or hepatitis C (HCV Ab).
• History of malignancy, excluding non-melanoma skin and cervical carcinoma in situ.
• Recent history (within the past year) or signs of alcohol or substance abuse.
• History of major psychiatric disorder.
• Female adult subjects who are pregnant or breastfeeding