Figure 2 shows changes in the incidence of invasive pneumococcal disease (IPD) among adults 19 through 64 years of age from 1998 through 2015 in the Unites States. Rates of IPD expressed as cases per 100,000 population are shown on the y-axis, and calendar year of surveillance on the x-axis. Blue bars represent overall IPD incidence, orange bars represent IPD incidence caused by serotypes included in the 23-valent pneumococcal polysaccharide vaccine (PPSV23), while the grey bars represent IPD incidence caused by serotypes included in the 13-valent pneumococcal conjugate vaccine. PPSV23, containing serotypes 1, 2, 3, 4, 5, 6B, 7F, 8, 9N, 9V, 10A, 11A, 12F, 14, 15B, 17F, 18C, 19A, 19F, 20, 22F, 23F, and 33F, has been available since 1984 and recommended for all adults 65 years or older and for people 2 years or older with chronic medical conditions. Pneumococcal 7-valent conjugate vaccine (PCV7), containing serotypes 4, 6B, 9V, 14, 18C, 19F, and 23F, was introduced for use among children