This is a Phase 1 first-in-human, randomized, controlled, observer-blinded study with a 2-arm parallel design. Healthy adults aged 18 to 49 years of age with no history of pneumococcal vaccination will be randomized equally to receive either a single intramuscular dose of multivalent pneumococcal conjugate vaccine or a licensed tetanus, diphtheria, acellular pertussis combination vaccine (Tdap) (control group).

Inclusion Criteria:

1. Male or female adults 18 to 49 years of age.
2. Healthy adults determined by medical history, physical examination, laboratory screening, and clinical judgment to be eligible for the study.
3. Negative serum pregnancy test for all female subjects who are of childbearing potential.

Exclusion Criteria:

1. Baseline laboratory test results outside of the normal reference range considered clinically significant.
2. History of severe adverse reaction and/or severe allergic reaction (eg, anaphylaxis) associated with a vaccine.
3. History of culture-proven invasive disease caused by S pneumoniae.
4. Previous vaccination with any licensed or investigational pneumococcal vaccine, or planned receipt through study participation.
5. Vaccination with diphtheria-, pertussis-, or tetanus-containing vaccine(s) from 12 months before investigational product administration, or planned receipt through study participation.
6. Male subjects and female subjects of childbearing potential who are unwilling or unable to use a highly effective method of contraception as outlined in this protocol for the duration of the study participation and for at least 6 months after the last dose of investigational product.