BACKGROUND - Invasive pneumococcal disease (IPD) rates decreased after 7-valent pneumococcal conjugate vaccine (PCV) introduction in 2000. We assessed whether previously described decreases were sustained.
METHODS - Active laboratory-based surveillance identified IPD cases in 5 Tennessee Counties. For each case, clinical data were collected, and antibiotic susceptibility testing and serotyping were performed. Penicillin resistance was defined as intermediate- or high-level resistance to penicillin. Serotypes were classified as PCV7, PCV13 (6 additional serotypes not in PCV7), pneumococcal polysaccharide vaccine (PPV23, 11 additional serotypes not in PCV13 and nonvaccine serotypes. Total and penicillin-resistant IPD rates were calculated for persons <2, 2-14 and ≥15 years of age before (1998 to 1999) and after (2001 to 2008) PCV7 introduction.
RESULTS - Annual IPD rates in children <2 years of age declined by 75% after PCV7 introduction (P < 0.001). Annual IPD rates in children 2-14 years of age declined by 51% after PCV7 introduction (P < 0.001). IPD rates in persons ≥15 of age years initially decreased 40% from 22 to 13 per 100,000 person-years (from 1998 through 2004), and then increased to 18 per 100,000 person-years in 2008. Both IPD and penicillin-resistant IPD PCV7 serotypes were almost completely eliminated in all age groups by 2008. During 2005 to 2008, 52.5%, 58% and 38% of IPD serotypes in children <2, 2-14 and ≥15 years of age, respectively, were the additional 6 serotypes in PCV13.
CONCLUSIONS - Overall, 9 years after PCV7 introduction both penicillin-susceptible and resistant IPD rates PCV7 serotypes have been nearly eliminated in Tennessee in all age groups. Total IPD rates remain reduced in children <15 years of age, whereas total IPD rates in persons ≥15 years of age have approached pre-PCV7 rates due to modest increases in nonvaccine serotypes.