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).