The actual number of deaths from the 2009 H1N1 pandemic might have been more than 15 times higher than previously thought, according to a study released on Monday.
When the new H1N1 virus, often referred to as swine flu, spread around the world three years ago, 18,500 deaths were reported to the World Health Organization in the first 16 months of the pandemic. Based on this new study, published online in The Lancet Infectious Diseases, researchers estimate 284,400 people actually died in the first year the virus was circulating around the world.
According to a model developed by the study authors, the actual number of deaths linked to the H1N1 flu virus could range anywhere from 151,700 to 575,400. Lead study author Dr. Fatimah Dawood says she and her colleagues used three types of data to come up with their estimates:
- The percentage of people who were sickened by H1N1 in 12 countries.
- The proportion of people who got sick from H1N1 and then went on to die (data that was only available from five countries).
- Previously published country-specific overall mortality rates.
Health officials recognize that the number of laboratory-confirmed flu deaths can considerably underestimate of the actual number of deaths from the flu. During the 2009 pandemic, many countries, particularly in Africa and Southeast Asia, lacked the ability to perform routine laboratory tests and therefore had difficulty identifying H1N1-related deaths.
While the WHO data suggests less than 12% of the confirmed deaths were in Africa and Southeast Asia, this new study estimates 51% of the deaths may have been from those two regions alone. According to these new calculations, Africa had the highest mortality rate, which was most likely influenced by the lack of access to health care and vaccines.
Dawood, a medical epidemiologist (also known as a disease detective) at the Centers for Disease Control and Prevention, says she hopes this research will help "limit the loss of human life in future pandemics."
She says it could be used to reduce the impact of outbreaks of new viruses worldwide, particularly in countries with fewer resources, and also help improve public health responses during pandemics in parts of the world that suffered more deaths.
Even though this study provides a larger number of deaths attributed to the H1N1 pandemic than previously thought, this flu outbreak was not nearly as deadly as some others.
Cécile Viboud (PhD) and Lone Simonsen (PhD), researchers at the National Institutes of Health who have studied the H1N1 pandemic, write in an accompanying commentary that the "2009 influenza pandemic was far from the doomsday scenario of a 1918-like pandemic that could have caused millions of deaths worldwide."
Still, the H1N1 virus had a significant impact on younger people.
This study estimates 80% of the deaths occurred in people younger than 65 - mostly in 18- to 64-year-olds - confirming what was seen by health officials during the earlier stages of the outbreak. In comparison, many deaths associated with seasonal flu are among the elderly, according to Dawood.