Impact of the H1N1 Flu Pandemic

H1N1 flu pandemic deaths in 2009 affected younger people more than elderly

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) In 2009, there were concerns across the world about the H1N1 flu. It turns out that, overall, death rates from this flu pandemic weren't worse than those of other flu seasons — at least for some.

A recent study estimated the worldwide deaths that occurred as a result of the H1N1 flu that season.

The researchers found that the death rates were about the same as in other years' flu seasons.

However, there were significant differences between who actually died in 2009 from the flu and who died during other flu seasons.

Most years, only about one in five individuals who died from the flu were under age 65, but during the 2009 pandemic, well over half the deaths that occurred were people under age 65.

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This study was led by Lone Simonsen, PhD, of the Department of Global Health at George Washington University School of Public Health and Health Services in Washington, DC.

Dr. Simonsen's team aimed to better understand what the actual death rates were from the H1N1 pandemic in 2009 to 2010.

The World Health Organization reported 18,631 deaths from laboratory-confirmed flu during the pandemic, but these were only the deaths reported directly to the WHO, which misses many more across the world.

The researchers therefore collected weekly reports of deaths and their causes from 2005 through 2009 from 20 different countries. Together, these countries comprised about 35 percent of the world population.

This data allowed the researchers to use mathematical models to estimate the death rates related to the flu from each of the countries that provided the reports.

Then the researchers determined the characteristics of these countries that matched other non-participating countries so that they could estimate the likely death toll from  the pandemic for all countries in the world.

The researchers were able to estimate that somewhere between 123,000 and 203,000 respiratory-caused deaths related to the pandemic occurred during the last nine months of 2009.

Well over half of these deaths (approximately 62 to 85 percent) occurred to individuals who were under 65 years old.

The death rates from the pandemic varied greatly across the world. Some countries in the Americas had rates that were more than 20 times higher than the death rates in Europe.

Using the data from the other years before 2009, the researchers estimated that a typical year would include about 148,000 to 249,000 deaths from influenza across the world. Among those deaths, however, only about 19 percent would be among individuals who were under 65 years old.

Therefore, the H1N1 pandemic of 2009 appeared to disproportionately affect younger individuals compared to the death rates from the flu in other years.

The researchers concluded that the actual death rates from the 2009 H1N1 flu pandemic were about 10 times greater than the count officially reported with the WHO.

"Although the pandemic mortality estimate was similar in magnitude to that of seasonal influenza, a marked shift toward mortality among persons under 65 years of age occurred, so that many more life-years were lost," the researchers wrote.

"The burden varied greatly among countries, corroborating early reports of far greater pandemic severity in the Americas than in Australia, New Zealand, and Europe," they wrote.

This study was published November 26 in the journal PLOS Medicine. The research was funded by the World Health Organization with NIVEL.

Additional support to the researchers came from the Science and Technology Directorate, Department of Homeland Security, the Fogarty International Center, the National Institutes of Health, the Medical Research Centre and the Bill & Melinda Gates Foundation

One author has consulted for GlaxoSmithKline (GSK) and served on advisory boards for GSK, Roche, Pfizer, Merck and Novartis. Two other authors own interest in Sage Analytica, which consults in epidemiology and bioinformatics.

Another author has consulted for GSK, and a final author has consulted for GSK, Novartis and MedImmune regarding the effectiveness of the flu vaccine.

Review Date: 
November 26, 2013
Last Updated:
November 28, 2013