The 2009 swine flu pandemic may have killed as many as 575,000 people, according to research.
Lancet Infectious Diseases journal claims that the real death toll of the H1N1 flu outbreak could be as much as 30 times higher than that of the 18,500 laboratory-confirmed deaths reported worldwide between April 2009 and August 2010 if the top estimate is taken.
The study was put together by a global team of researchers, who explain that laboratory-confirmed death tolls are always significantly lower than the real figure.
The team developed a model using influenza-specific data from 12 low, middle and high-income countries, which hypothesises that the risk of flu death was higher in certain countries than in others that were more developed, before using data provided by the World Health Organisation on lower respiratory tract mortality to account for the differences.
The authors were only able to acquire data from countries that kept data on the numbers of people who developed flu symptoms and flu deaths during the pandemic, but low and middle-income countries were notably low on data. Because of the shortage of precise data the authors suggest an estimated death toll of 15 times higher than previous estimates.
Despite the lack of certainty about the figures, the study reveals the shocking reality behind the 2009 outbreak, as well as reigniting fears over the potential human cost of another pandemic. Newly released mortality data from Mexico suggests that the toll in that country even exceeded the study's estimates.
Lead author Dr Fatimah Dawood said: "The study underscores the significant human toll of an influenza pandemic. We hope that this work can be used not only to improve influenza disease burdens modelling globally, but to improve the public health response during future pandemics in parts of the world that suffer more deaths, and to increase the public's awareness of the importance of influenza prevention."
The study concludes: "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-assciated mortality during future pandemics."
The first known victim of the swine flu pandemic was infected in central Mexico in March 2009. It took the disease just one month to cross the border to the US and reach California.
Before long, it had spread to 74 countries and was officially declared a pandemic. According to the study findings, the majority of the victims died in Africa, with children most likely to be infected.
Because so many of the sufferers were children, swine flu cost more than three times as many years of life, 9.7 million, than seasonal flu outbreaks, which would typically cost 2.8 million years.