Estimating the population-level impact of vaccines using synthetic controls.
When a new vaccine is introduced, it is critical to monitor trends in disease rates to ensure that the vaccine is effective and to quantify its impact. However, estimates from observational studies can be confounded by unrelated changes in healthcare utilization, changes in the underlying health of the population, or changes in reporting. Other diseases are often used to detect and adjust for these changes, but choosing an appropriate control disease a priori is a major challenge. The "synthetic controls" (causal impact) method, which was originally developed for website analytics and social sciences, provides an appealing solution. With this approach, potential comparison time series are combined into a composite and are used to generate a counterfactual estimate, which can be compared with the time series of interest after the intervention. We sought to estimate changes in hospitalizations for all-cause pneumonia associated with the introduction of pneumococcal conjugate vaccines (PCVs) in five countries in the Americas. Using synthetic controls, we found a substantial decline in hospitalizations for all-cause pneumonia in infants in all five countries (average of 20%), whereas estimates for young and middle-aged adults varied by country and were potentially influenced by the 2009 influenza pandemic. In contrast to previous reports, we did not detect a decline in all-cause pneumonia in older adults in any country. Synthetic controls promise to increase the accuracy of studies of vaccine impact and to increase comparability of results between populations compared with alternative approaches.
Department of Epidemiology of Microbial Diseases, Yale University School of Public Health, New Haven, CT 06520.
Christian A W
CA
Bruhn
Sage Analytica, Portland, ME 04101.
Stephen
S
Hetterich
Sage Analytica, Portland, ME 04101.
Cynthia
C
Schuck-Paim
Department of Epidemiology of Microbial Diseases, Yale University School of Public Health, New Haven, CT 06520.|Department of Statistics, University of California, Riverside, CA 92521.
Esra
E
Kürüm
Sage Analytica, Portland, ME 04101.
Robert J
RJ
Taylor
Sage Analytica, Portland, ME 04101.
Roger
R
Lustig
Department of Epidemiology of Microbial Diseases, Yale University School of Public Health, New Haven, CT 06520.|Department of Pediatrics, Yale School of Medicine, New Haven, CT 06520.
Eugene D
ED
Shapiro
Department of Epidemiology of Microbial Diseases, Yale University School of Public Health, New Haven, CT 06520.|Department of Biostatistics, Yale School of Public Health, New Haven, CT 06520.
Joshua L
JL
Warren
Sage Analytica, Portland, ME 04101.|Milken Institute School of Public Health, George Washington University, Washington, DC 20052.|Department of Public Health, University of Copenhagen, 1017 Copenhagen, Denmark.
Lone
0000-0003-1535-8526
L
Simonsen
Department of Epidemiology of Microbial Diseases, Yale University School of Public Health, New Haven, CT 06520; daniel.weinberger@yale.edu.
Daniel M
DM
Weinberger
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D015982:Bias; D002648:Child; D002675:Child, Preschool; D015986:Confounding Factors, Epidemiologic; D035061:Control Groups; D005260:Female; D062489:Health Impact Assessment / Q000379:methods / Q000706:statistics & numerical data*; D006760:Hospitalization / Q000706:statistics & numerical data*; D006801:Humans; D007223:Infant; D007843:Latin America / Q000453:epidemiology; D008297:Male; D008875:Middle Aged; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000517:prevention & control; D022242:Pneumococcal Vaccines; D011014:Pneumonia / Q000453:epidemiology / Q000209:etiology / Q000517:prevention & control*; D014481:United States / Q000453:epidemiology; D014611:Vaccination / Q000706:statistics & numerical data; D018074:Vaccines, Conjugate; D055815:Young Adult
D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate
Streptococcus pneumoniae; observational study; pneumococcal conjugate vaccines; program evaluation; synthetic controls