The 2009 swine flu pandemic may have killed 284,500 people globally, 15 times more people than reported at the time, according to the first report to estimate the death toll.
The study, published on Tuesday by the journal Lancet Infectious Diseases, focused on figures in poorer countries and found that the H1N1 influenza virus may even be responsible for as many as 579,000, a drastic difference from the original count set by the World Health Organization at 18,500.
Researchers from the U.S. Centers for Disease Control and Prevention (CDC) estimate that around 51 percent of swine flu deaths may have occurred in Southeast Asia or Africa, which only account for 38 percent of the world's population.
"Unlike most other mortality estimates for the 2009 pandemic, this study includes estimated mortality for countries in southeast Asia and Africa where surveillance data on influenza-associated mortality are limited," said lead researcher Dr. Fatimah Dawood of the CDC, according to AFP.
Scientists attributed the huge discrepancy between the latest and original estimates to the simple tabulation of laboratory confirmed cases, which are known to be significantly lower than the number of deaths that actually occur.
Cecile Viboud of the National Institutes of Health and Lone Simonsen of George Washington University, who were not involved in the study, wrote in an editorial accompanying the study that the estimate shows the difficulty in tracking the influence of the pandemic as it's still going on.
They wrote that the WHO was criticized for exaggerating the H1N1 threat had already warned that the death toll would end up being “unquestionably higher” than what the agency was able to confirm, which was based on what was 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.
Scientists developed a mathematical model using data from 12 countries on flu cases diagnosed by the patients symptoms alone and not by a laboratory test, and they also estimated that the mortality risk is higher is some countries compared to others.
Researchers noted that the lack of available data in poorer countries may affect the accuracy of their estimates.
"This pandemic really did take an enormous toll," said Dawood, according to Reuters. "Our results also suggest how best to deploy resources. If a vaccine were to become available, we need to make sure it reached the areas where the death toll is likely to be highest."
"Our findings emphasize the need to improve the global response to future influenza pandemics and expand production and improve delivery of influenza vaccines to Africa and Southeast Asia because these countries might have borne a disproportionate burden of pandemic mortality during the first year of virus circulation," Dawood and colleagues wrote.
The swine flu pandemic, caused by the H1N1 influenza virus, first emerged in April 2009 in Mexico and lasted to August 2010. During that time, the Americans were warned not to travel to Mexico, where the first known swine flu case was reported and Egypt ordered the slaughter of all the country's pigs in an attempt to contain the virus even though the infection travels from person to person.
Researchers wrote "continued efforts to strengthen influenza surveillance worldwide, particularly for influenza-associated mortality, are needed both to guide seasonal influenza prevention strategies and to build influenza surveillance systems to provide better and more timely and globally representative data for influenza-associated mortality during future pandemics."