Global Mortality Estimates for the 2009 Influenza Pandemic from the GLaMOR Project: A Modeling Study

Background: Assessing the mortality impact of the 2009 influenza A H1N1 virus (H1N1pdm09) is essential for optimizing public health responses to future pandemics. The World Health Organization reported 18,631 laboratory-confirmed pandemic deaths, but the total pandemic mortality burden was substantially higher. We estimated the 2009 pandemic mortality burden through statistical modeling of mortality data from multiple countries. Methods and Findings: We obtained weekly virology and underlying cause-of-death mortality time series for 2005–2009 for 20 countries covering ,35% of the world population. We applied a multivariate linear regression model to estimate pandemic respiratory mortality in each collaborating country. We then used these results plus ten country indicators in a multiple imputation model to project the mortality burden in all world countries. Between 123,000 and 203,000 pandemic respiratory deaths were estimated globally for the last 9 mo of 2009. The majority (62%–85%) were attributed to persons under 65 y of age. We observed a striking regional heterogeneity, with almost 20-fold higher mortality in some countries in the Americas than in Europe. The model attributed 148,000–249,000 respiratory deaths to influenza in an average prepandemic season, with only 19% in persons ,65 y. Limitations include lack of representation of low-income countries among single-country estimates and an inability to study subsequent pandemic waves (2010–2012). Conclusions: We estimate that 2009 global pandemic respiratory mortality was ,10-fold higher than the World Health Organization’s laboratory-confirmed mortality count. Although the pandemic mortality estimate was similar in magnitude to that of seasonal influenza, a marked shift toward mortality among persons ,65 y of age occurred, so that many more life-years were lost. The burden varied greatly among countries, corroborating early reports of far greater pandemic severity in the Americas than in Australia, New Zealand, and Europe. A collaborative network to collect and analyze mortality and hospitalization surveillance data is needed to rapidly establish the severity of future pandemics. Please see later in the article for the Editors’ Summary. Citation: Simonsen L, Spreeuwenberg P, Lustig R, Taylor RJ, Fleming DM, et al. (2013) Global Mortality Estimates for the 2009 Influenza Pandemic from the GLaMOR Project: A Modeling Study. PLoS Med 10(11): e1001558. doi:10.1371/journal.pmed. 1001558 Academic Editor: Simon I. Hay, University of Oxford, United Kingdom Received February 26, 2013; Accepted October 15, 2013; Published November 26, 2013 Copyright: 2013 Simonsen et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This study was supported by the WHO on a contract with NIVEL (APW 20043611 and 200617995). LS acknowledges support from the RAPIDD (Research and Policy for Infectious Disease Dynamics) program of the Science and Technology Directorate, Department of Homeland Security, the Fogarty International Center, and National Institutes of Health. MDVK acknowledges salary support from the Medical Research Centre and the Bill & Melinda Gates Foundation. No funding bodies had any role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: LS has provided consultancy services to GlaxoSmithKline (GSK) and served on expert advisory boards for GSK, Roche, Pfizer, Merck, and Novartis. LS and RJT have an ownership interest in Sage Analytica, a consultancy in epidemiology and bioinformatics. DMF has provided consultancy services for GSK, Novartis, and MedImmune relating to influenza epidemiology and vaccine effectiveness and has been supported to attend international influenza meetings. WJP has served on an influenza advisory board for GSK. Abbreviations: GLaMOR, Global Pandemic Mortality; GNI, gross national income; H1N1pdm09, 2009 influenza A H1N1 pandemic; ICD-10, International Classification of Diseases–10; WHO, World Health Organization. * E-mail: lone@gwu.edu " Membership of the GLaMOR Collaborating Teams is provided in the Acknowledgments. PLOS Medicine | www.plosmedicine. org 1 November 2013 | Volume 10 | Issue 11 | e1001558