The 2009 swine flu pandemic may have killed 15 times more people globally than reported at the time, according to the first study to estimate the death toll.
The H1N1 influenza virus probably killed about 284,500 people worldwide, compared with 18,500 deaths reported to the World Health Organization, researchers from the U.S. Centers for Disease Control and Prevention wrote in the journal Lancet Infectious Diseases today. More than half the deaths may have been in southeast Asia and Africa, compared with 12 percent of officially reported fatalities, the authors wrote.
The estimate shows the difficulty in tracking the effect of a pandemic as it’s unfolding, Cecile Viboud of the National Institutes of Health and Lone Simonsen of George Washington University wrote in an editorial. The WHO, which was criticized for exaggerating the H1N1 threat, said during the outbreak that the toll would end up being “unquestionably higher” than that reported to it by national authorities.
“Laboratory-confirmed deaths are gross underestimates of influenza-related mortality because of the lack of routine laboratory tests and difficulties in identification of influenza-related deaths,” they wrote.
The H1N1 virus was reported in more than 214 countries through August 2010, when the WHO declared an end to the pandemic. It’s since become one of three seasonal flu strains circulating worldwide, causing infections mostly during the winter months.
Seasonal influenza kills as many as 500,000 people every year, according to the Geneva-based WHO. Those estimates are typically based on the number of deaths above a country’s normal death rate that coincide with a flu season.
Researchers led by Fatimah Dawood at the Atlanta-based CDC’s influenza division developed a mathematical model using data from 12 countries on flu cases that were diagnosed by a patient’s symptoms alone, and not by a laboratory test. They hypothesized that the risk of death is higher in some countries than others.
Shortcomings in the availability of data in poorer countries may affect the accuracy of the estimates, they said.
The number of deaths from the pandemic highlights the need to expand production and improve delivery of vaccines to poorer countries, which are often hardest hit by pandemics and lack the resources to monitor diseases, the researchers wrote.
“The study underscores the significant human toll of an influenza pandemic,” Dawood and colleagues said in an e-mailed statement. “We hope that this work can be used not only to improve influenza disease burden modeling globally, but to improve the public health response during future pandemics in parts of the world that suffer more deaths.”
Eighty percent of the deaths were probably in people younger than 65 years, the authors wrote.