Decline in pneumonia admissions after routine childhood immunisation with pneumococcal conjugate vaccine in the USA: a time-series analysis

Abstract

Routine infant immunisation with seven-valent pneumococcal conjugate vaccine (PCV7) began in the USA in 2000. Although invasive pneumococcal disease has declined substantially, the programme's effect on hospital admissions for pneumonia is unknown. We therefore assessed the effect of the programme on rates of all-cause and pneumococcal pneumonia admissions. Data from the Nationwide Inpatient Sample, the largest inpatient database available in the USA, were analysed with an interrupted time-series analysis that used pneumonia (all-cause and pneumococcal) admission rates as the main outcomes. Monthly admission rates estimated for years after the introduction of PCV7 vaccination (2001-2004) were compared with expected rates calculated from pre-PCV7 years (1997-1999). The year of vaccine introduction (2000) was excluded, and rates of admission for dehydration were assessed for comparison. At the end of 2004, all-cause pneumonia admission rates had declined by 39% (95% CI 22-52) for children younger than 2 years, who were the target population of the vaccination programme. This annual decline in all-cause pneumonia admissions of 506 (291-675) per 100,000 children younger than 2 years represented about 41,000 pneumonia admissions prevented in 2004. During the 8 study years, 10,659 (2%) children younger than 2 years admitted with pneumonia were coded as having pneumococcal disease; these rates declined by 65% (47-77). This decline represented about 17 fewer admissions per 100,000 children in 2004. Admission rates for dehydration for children younger than 2 years remained stable over the study period. The reduction in all-cause pneumonia admissions in children younger than 2 years provides an estimate of the proportion of childhood pneumonias attributable to Streptococcus pneumoniae in the USA that are vaccine preventable. Our results contribute to the growing body of evidence supporting the beneficial effects of the pneumococcal conjugate vaccines in children.