Objective. To determine the population impact of pneumococcal conjugate vaccine (PCV) on pneumococcal-related diseases, including pneumonia and otitis media.

Methods. Using administrative data from Tennessee Medicaid and 3 commercial insurance plans in upstate New York, we measured annual rates of medical visits for pneumococcal-related diseases (pneumococcal and nonspecific pneumonia and invasive disease; otitis media) and pneumococcal-unrelated diseases (other acute respiratory illnesses). Disease rates before (1995–2000 in Tennessee; 1998–2000 in New York) and after (2000–2002) PCV licensure were calculated for children aged <2 years (eligible for PCV) and those 3 to 5 years (not routinely given PCV). Because annual variations should affect both age groups similarly and vaccine-related outcomes should preferentially decline in younger children, ratios (<2:3–5 years) of disease rates before and after PCV licensure were compared. Expected disease rates were calculated for children aged <2 years in each postvaccine year. The difference between observed and expected disease rates was the estimated vaccine effect.

Results. In 2001–2002, there were 67 380 and 9485 child-years of observation for Tennessee and New York children aged <2 years, respectively. We observed fewer visits for pneumonia and invasive disease per 1000 children than expected in both regions: 20 fewer emergency department or outpatient visits in Tennessee and 33 fewer outpatient visits in New York. Otitis media visits declined by 118 and 430 per 1000 children in Tennessee and New York, respectively.

Conclusions. Adding PCV to the childhood immunization schedule was associated with a 10-fold greater reduction in pneumonia and a 100-fold greater reduction in otitis media than the previously reported reduction in culture-confirmed invasive pneumococcal diseases of 1.3 episodes per 1000 children aged <2 years. Although additional studies are needed to confirm the impact of routine immunization with PCV on pneumococcal-related disease, these results suggest that its impact is substantially greater than the effects on invasive disease alone.

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