Changing Epidemiology of Invasive Pneumococcal Disease Among Older Adults in the Era of Pediatric Pneumococcal Conjugate Vaccine

Abstract

CONTEXT: A conjugate vaccine targeting 7 pneumococcal serotypes was licensed for young children in 2000. In contrast to the 23-valent polysaccharide vaccine used in adults, the 7-valent conjugate vaccine affects pneumococcal carriage and transmission. Early after its introduction, incidence of invasive pneumococcal disease declined among older adults, a group at high risk for pneumococcal disease. OBJECTIVE: To determine among adults aged 50 years or older whether incidence of invasive pneumococcal disease, disease characteristics, or the spectrum of patients acquiring these illnesses have changed over the 4 years since pneumococcal conjugate vaccine licensure. DESIGN, SETTING, AND POPULATION: Population-based surveillance of invasive pneumococcal disease in 8 US geographic areas (total population, 18,813,000), 1998-2003. MAIN OUTCOME MEASURES: Incidence of invasive pneumococcal disease by pneumococcal serotype and other characteristics; frequency among case patients of comorbid conditions and other factors influencing mortality. RESULTS: Incidence of invasive pneumococcal disease among adults aged 50 years or older declined 28% (95% confidence interval [CI], -31% to -24%), from 40.8 cases/100,000 in 1998-1999 to 29.4 in 2002-2003. Among those aged 65 years or older, the 2002-2003 rate (41.7 cases/100,000) was lower than the Healthy People 2010 goal (42 cases/100,000). Among adults aged 50 years or older, incidence of disease caused by the 7 conjugate vaccine serotypes declined 55% (95% CI, -58% to -51%) from 22.4 to 10.2 cases/100,000. In contrast, disease caused by any of the 16 serotypes only in polysaccharide vaccine did not change, and disease caused by serotypes not in either vaccine increased somewhat, from 6.0 to 6.8 cases/100,000 (13%; 95% CI, 1% to 27%). Between 1998-1999 and 2002-2003, the proportion of case-patients with human immunodeficiency virus infection increased from 1.7% (47/2737) to 5.6% (124/2231) (P<.001), and those with any comorbid condition that is an indication for pneumococcal polysaccharide vaccination increased from 62.3% (1842/2955) to 72.0% (1721/2390) (P<.001). CONCLUSIONS: Our findings indicate that use of conjugate vaccine in children has substantially benefited older adults. However, persons with certain comorbid conditions may benefit less than healthier persons from the indirect effects of the new vaccine.