Although preventing pneumococcal disease in adults—specifically, adults 65 years or older and adults with immunodeficiencies—is a clinical and public health priority in the United States, current vaccines are inadequate. It is estimated that Streptococcus pneumoniae causes more than 400 000 hospitalizations and more than 16 000 deaths from pneumonia annually among adults in the United States, costing more than $1 billion.1 These numbers are likely to increase substantially in the coming decades.1 At present, the Advisory Committee on Immunization Practices of the Centers for Disease Control and Prevention recommends that older adults and adults who are immunocompromised receive a dose of pneumococcal protein-polysaccharide conjugate vaccine (PCV13) followed by a dose of pneumococcal polysaccharide vaccine (PPV23).2,3 These vaccines target 13 and 23, respectively, of the more than 90 different pneumococcal serotypes; 12 of the serotypes in PCV13 are also included in PPV23. Use of these vaccines in adults, however, has limited effectiveness. A new, adult-specific conjugate vaccine targeting the serotypes that most commonly cause pneumococcal disease could offer substantially greater protection than PCV13 and PPV23 can.