The 2009 H1N1 epidemic was 10 times worse than we thought

The H1N1 flu pandemic of 2009 killed as many as 203,000 people across the globe, about 10 times more than previously estimated by the World Health Organization (WHO), according to a report in PLOS Medicine.

In 2010, WHO reported that there were just 18,500 deaths related to the pandemic based on the number of laboratory-confirmed cases. The low estimate led many to wonder if the perils of H1N1 had been overblown, but most people infected with the strain never got lab confirmation of their diagnosis.

"We knew all along that lab-confirmed deaths were just the tip of the iceberg," says University of Minnesota's Michael Osterholm, one of the epidemiologists working on the report.

CDC: H1N1 was deadlier than initially estimated

For the report, led by George Washington University School of Public Health and funded by WHO, 60 researchers used data on respiratory deaths to calculate a new global mortality rate for the pandemic. They determined that the global death toll was between 123,000 and 203,000.

According to lead author Lone Simonsen, the research revealed that the "mortality burden of this pandemic fell most heavily on younger people." About 90% of mortalities occur in people over age 65 with a seasonal flu, but about 62% to 85% of H1N1 deaths were among those under age 65.

Researchers also found that mortalities were more concentrated in Central America and South America than previously thought; the death tolls in those regions were nearly 20 times higher than in Europe (Szabo, USA Today, 11/26; Gholipour, CBS News/Live Science, 11/27; Morin, "Science Now," Los Angeles Times, 11/26).