H1N1 Pandemic May Have Killed Nearly 300,000 (CME/CE)

By Todd Neale, , MedPage TodayPublished: June 25, 2012Reviewed by Zalman S. Agus, MD; Emeritus Professor, Perelman School of Medicine at the University of Pennsylvania

But the estimate spans a range as low as 151,700 and as high as 575,400 during the first year of virus circulation, Fatimah Dawood, MD, of the CDC’s influenza division in Atlanta, and colleagues reported on-line in The Lancet Infectious Diseases.

Most of the deaths occurred in individuals younger than 65 (80%) and in Africa and Southeast Asia (59%).

“Our findings accentuate the need to improve the global response to future influenza pandemics and expand production and improve delivery of influenza vaccines to Africa and Southeast Asia because these countries might have borne a disproportionate burden of pandemic mortality during the first year of virus circulation,” Dawood and colleagues wrote.

From April 2009 — when the pandemic strain first emerged — to August 2010, the World Health Organization received 18,500 reports of deaths from lab-confirmed H1N1 infections. Looking only at lab-confirmed cases is known to underestimate the actual numbers of deaths, and influenza mortality is usually tracked with statistical modeling.

Dawood and colleagues developed a new technique to estimate deaths from the pandemic strain.

They first calculated crude respiratory mortality rates using cumulative virus-associated symptomatic attack rates from 12 countries and symptomatic case fatality ratios from five high-income countries, and then adjusted for between-country differences in the likelihood of dying from influenza.

The researchers also estimated cardiovascular disease mortality rates associated with the pandemic by multiplying the ratio of excess deaths from cardiovascular disease to excess deaths from respiratory diseases by the crude respiratory disease mortality rate associated with the new virus.

Those techniques yielded an estimated 201,200 respiratory deaths and 83,300 cardiovascular deaths associated with the pandemic virus from April 2009 to August 2010.

Because the new H1N1 strain disproportionately affected the younger population, the number of years of life lost was greater during the pandemic than during seasonal epidemics.

Even so, the findings “confirm that the 2009 influenza pandemic was far from the doomsday scenario of a 1918-like pandemic that could have caused millions of deaths worldwide,” according to Cécile Viboud, PhD, of the NIH’s Fogarty International Center in Bethesda, Md., and Lone Simonsen, PhD, of the George Washington University School of Public Health and Health Services in Washington, D.C.

“However,” they wrote in an accompanying comment, “the model was based on several assumptions, and therefore validation of the results against independent estimates available from a handful of countries is crucial.”

The researchers acknowledged that there are some limitations to their technique, including the relative dearth of globally representative estimates of symptomatic attack rates and symptomatic case fatality ratios.

Dawood and colleagues reported that they had no conflicts of interest.

Simonsen is a co-principal investigator of the WHO-funded project to estimate the regional and global burden of the pandemic based on the excess mortality approach, and Viboud is a collaborator and member of the WHO oversight committee for this project. This work was supported by the in-house influenza research program of the Division of International Epidemiology and Population Studies, Fogarty International Center, NIH, which is funded by the International Influenza Unit, Office of Global Affairs, Department of Health and Human Services. Simonsen acknowledged support from the RAPIDD program of the Science and Technology Directorate, Department of Homeland Security.

, MedPage Today Staff Writer, got his begin in journalism at Audubon Magazine and made a stop in directory publishing before landing at MedPage Today. He received a B.S. in biology from the University of Massachusetts Amherst and an M.A. in journalism from the Science, Health, and Environmental Reporting program at New York University. He is based at MedPage Today headquarters in Little Falls, N.J.

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