The goal of this clinical trial is to learn if whole-cell Streptococcus pneumoniae (wSp) vaccination is safe and tolerated in healthy adults. The main aim is to evaluate the safety and tolerability of wSp vaccine.

Researchers will compare wSp vaccinated participants with placebo-treated participants.

Participants will be administered once with 1mg wSp vaccine or placebo. After dosing, they will be followed up for 30 days. In addition to the screening and enrollment visits, each participant will come to the study site for scheduled study visits on Days 14 and 30 to undergo study evaluations and measurements and to monitor safety. Each participant also will receive scheduled phone calls on Days 3 and 7 to monitor safety.

Inclusion Criteria:

• Adult aged > 18 and < 49 years at screening.
• Body mass index (BMI) ≥ 18.0 and ≤ 30.0 kg/m2, with a maximum body weight of 120 kg at screening.
• Good general health, without significant medical illness or abnormal physical examination, or laboratory findings per PI discretion.
• If female, not breastfeeding, not pregnant, and not planning pregnancy during study period.
• If female of child-bearing potential, willing to use acceptable method of contraception.
• Willing and able to comply with all study activities, assessments, and restrictions through 30 days of follow-up. Willing and able to be contacted reliably by phone, and willing for the study team to record phone voice messages as needed.
• Provided written informed consent to participate in the clinical trial before any study-related activities are carried out and, in the PI's opinion, must be able to understand the full nature and purpose of the trial, including possible risks and adverse effects.

Exclusion Criteria:

In addition to meeting the inclusion criteria, individuals will be excluded from this trial if they meet any of the following exclusion criteria:

• History or presence of clinically significant medical condition or disease, including (but not limited to) clinically significant cardiovascular, pulmonary, hepatic, renal, gastrointestinal, endocrine, hematologic, immunologic, oncologic, rheumatologic, dermatologic, neurological or psychiatric disease.
• History of known invasive pneumococcal disease.
• History of congenital or acquired immunodeficiency.
• Any acute illness within 72 hours prior to randomization.
• Abnormal vital sign(s) or laboratory test result(s) deemed clinically relevant, as determined by the PI.
• Known allergy or previous anaphylaxis to any components of the study product or contraindication to intramuscular (IM) injection (e.g., history of bleeding disorder).
• Previous enrollment in this trial or received other investigational vaccines, drugs, or products within the past 12 weeks, or intend to participate in another clinical trial during the duration of this trial.
• Received any vaccine within the past 4 weeks.
• Received any immunomodulating or immunosuppressive agent or medicine, including over-the-counter, herbal and prescription drugs and supplements within the past 12 weeks or anticipate needing within the study period.
• Received blood or blood products within the past 12 weeks or anticipate needing within the study period.
• Current use of over the counter or prescription drugs of known hepatotoxicity.
• Current or history of alcohol or drug dependence or abuse.
• Any condition (medical, psychiatric, or behavioral) that in the opinion of the PI, would increase the participant's health risks in study participation or would increase the risk of not achieving the study's objectives.
• Unable or unwilling to provide adequate informed consent.