Death toll from 2009 H1N1 outbreak was much higher than previous estimates

While there were 18,500 laboratory-confirmed deaths due to the H1N1 influenza outbreak in 2009, new estimates from an international group of researchers indicate more than half a million people worldwide may actually have died as a result of the flu.

According to researchers, an estimated 151,700 to 575,400 people died as a result of the swine flu outbreak during the first year alone – meaning the death toll may have been 15 times higher than what was reported by the World Health Organization.  The researchers addressed the discrepancy, explaining that lab-confirmed flu deaths are known to be significantly lower than the number of deaths that actually occur.

They said they arrived at their own estimates by developing a new model that looked at data from 12 low, middle and high-income countries.  The countries included in the model had tracked the number of people who developed flu symptoms as well as the number of deaths among flu cases during the 2009 pandemic.

“There are several challenges to estimating global mortality of the influenza pandemic,” study leader Dr. Fatimah Dawood from the Centers for Disease Control and Prevention, told FoxNews.com.  “The data is sparse in some countries of the word because the tracking varies from country to country, and also the severity of the flu’s impact ranged by region.”

Nevertheless, Dawood said it was important to try to get as accurate estimates as possible both to quantify the impact of the pandemic on the global population and to plan for future pandemics – in part, by studying the regional distribution of flu deaths.

According to the researchers, 59 percent of the deaths appear to have occurred in southeast Asia and Africa, regions that are home to 38 percent of the world’s population.  The highest mortality rates occurred in Africa, the researchers said.

“In future pandemic planning, this really highlights the need to ensure that influenza prevention tools are available to all regions to limit the loss of life,” Dawood said.  “Historically, the capacity to produce vaccines in those regions (southeast Asia and Africa) have been limited, but there have been ongoing efforts to strengthen that capacity, so we need to continue that work."

The results also indicated that 80 percent of the deaths occurred in people younger than 65, a turnaround from seasonal influenza in which 80 to 90 percent of deaths occur in the elderly.

“Looking just at the number of deaths is not all of the story,” Dawood said.  “When you start to think about the number of potential years of life lost, it’s substantially higher that what is anticipated during a typical flu season.”

According to Dawood, one of the hypotheses for why the H1N1 virus had so little impact on the elderly is because a similar H1N1 virus circulated before 1957, which may mean that elderly people could have had a pre-existing immunity to the 2009 virus and therefore had lower rates of infection.

The study was published in the journal The Lancet.