Global seasonal influenza mortality estimates: a comparison of 3 different approaches.

Background Prior to updating global influenza-associated mortality estimates, the World Health Organization convened a consultation in July 2017 to understand differences in methodology and implications on results of three influenza mortality projects from the United States Centers for Disease Control and Prevention (CDC), the Netherlands Institute for Health Service Research (GLaMOR), and the Institute for Health Metrics and Evaluation (IHME). The expert panel reviewed estimates and discussed differences in data sources, analysis, and modeling assumptions. Method We performed a comparison analysis of the estimates. Influenza-associated respiratory death counts were comparable between CDC and GLaMOR; IHME estimate was considerably lower. Results The greatest country-specific influenza-associated mortality rate fold differences between CDC/IHME and between GLaMOR/IHME estimates were among countries in South-East Asia and Eastern Mediterranean region. The data envelope used for the calculation was one of the major differences (CDC and GLaMOR: all respiratory deaths; IHME: low respiratory infection deaths). With the assumption that there is only one cause of death for each death, IHME estimates a fraction of the full influenza-associated respiratory mortality that is measured by the other two groups. Wide variability of parameters was observed. Conclusion Continued coordination between groups could assist with better understanding of methodological differences and new approaches to estimating influenza deaths globally