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Epidemiology. 2017 Nov;28(6):889-897. doi: 10.1097/EDE.0000000000000719.

Bayesian Model Averaging with Change Points to Assess the Impact of Vaccination and Public Health Interventions.

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From the aDepartment of Statistics, University of California, Riverside, CA; bDepartment of Biostatistics, Yale School of Public Health, New Haven, CT; cSage Analytica, Bethesda, MD; dDepartment of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT; eDpto. de Epidemiología, DIPLAS, Ministerio de Salud, Chile; and fDepartment of Global Health, Milken Institute School of Public Health, George Washington University, Washington, DC.



Pneumococcal conjugate vaccines (PCVs) prevent invasive pneumococcal disease and pneumonia. However, some low-and middle-income countries have yet to introduce PCV into their immunization programs due, in part, to lack of certainty about the potential impact. Assessing PCV benefits is challenging because specific data on pneumococcal disease are often lacking, and it can be difficult to separate the effects of factors other than the vaccine that could also affect pneumococcal disease rates.


We assess PCV impact by combining Bayesian model averaging with change-point models to estimate the timing and magnitude of vaccine-associated changes, while controlling for seasonality and other covariates. We applied our approach to monthly time series of age-stratified hospitalizations related to pneumococcal infection in children younger 5 years of age in the United States, Brazil, and Chile.


Our method accurately detected changes in data in which we knew true and noteworthy changes occurred, i.e., in simulated data and for invasive pneumococcal disease. Moreover, 24 months after the vaccine introduction, we detected reductions of 14%, 9%, and 9% in the United States, Brazil, and Chile, respectively, in all-cause pneumonia (ACP) hospitalizations for age group 0 to <1 years of age.


Our approach provides a flexible and sensitive method to detect changes in disease incidence that occur after the introduction of a vaccine or other intervention, while avoiding biases that exist in current approaches to time-trend analyses.

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