Trends in U.S. hospitalizations and inpatient deaths from pneumonia and influenza, 1996-2011

Abstract

Background: To reduce excess morbidity and mortality of pneumonia and influenza (PI), the Advisory Committee on Immunization Practices has recommended the use of 7-valent pneumococcal conjugate vaccine (PCV7), and incrementally expanded the target group for annual influenza vaccination of healthy persons, to ultimately include all persons ≥6 months of age without contraindications as of the 2010-2011 influenza season. We aimed to capture broader epidemiologic changes by looking at PI collectively.

Methods: Using interrupted time series, we evaluated the changes in the rates of PI hospitalization and inpatient death across three periods defined according to the changes in vaccination policy. We assessed linear trends adjusting for seasonality, sex, and age group, allowing for differential impact across age groups. PI hospitalizations were defined as a principal diagnosis of PI, or a principal diagnosis of sepsis or respiratory failure, accompanied by a secondary diagnosis of PI.

Results: Overall annual rates of PI hospitalizations and inpatient deaths declined by 95 per 100,000 (95% CI: 45-145) and by 4.4 per 100,000 (95% CI: 0.9-7.8), respectively. This translates to 295,000 fewer PI hospitalizations and 13,600 fewer PI inpatient deaths than expected based on the average rates from 1996 through 1999. PI hospitalizations dropped the most among seniors aged 65+ by 487 per 100,000, followed by children aged <2, by 228 per 100,000. PI inpatient deaths declined most among seniors aged 65+, by 25.3 per 100,000.

Conclusions: In this nationally representative study, PI hospitalizations and inpatient deaths decreased in U.S. between 1996 and 2011. There is a temporal association with the introduction and widespread use of pneumococcal conjugate vaccines, and the expansion of the target group for annual influenza vaccination to include all persons ≥6 months of age, while it is difficult to attribute these changes directly to specific vaccines used in this era.

Keywords: Influenza vaccine; Pneumococcal conjugate vaccine; Pneumonia and influenza; Vaccination policy.