The death toll from the 2009 H1N1 “swine flu” pandemic may be 15 times higher than the number of laboratory-confirmed deaths previously reported to the World Health Organization (WHO), according to an article published online today in The Lancet Infectious Diseases.
The article says that while estimates of 2009 H1N1-associated deaths have been derived for some countries such as the USA, these are the first estimates of the worldwide number of deaths caused by the pandemic.
During the pandemic, 18,500 laboratory-confirmed H1N1-deaths were reported worldwide from April 2009 to August 2010.
However, the number of lab-confirmed flu deaths is known to be significantly lower than the number of flu deaths that actually occur.
The new research indicates that an estimated 151,700 to 575,400 people died as a result of having contracted 2009 H1N1 during the first year that the virus circulated in each country worldwide.
To arrive at their estimates, a global team of researchers developed a new model that used influenza-specific data from 12 low, middle, and high-income countries.
They hypothesised that risk of death from flu is higher in some countries than others, and used WHO data on lower respiratory tract mortality in different countries to account for these differences.
The authors calculated that globally there were 201,200 respiratory deaths with an additional 83,300 cardiovascular deaths associated with 2009 pandemic influenza A H1N1 – collectively around 15 times higher than the official figures.
The new estimates of flu deaths are based only on data from countries that hold information on the numbers of people who developed flu symptoms as well as the numbers of deaths among flu cases during the 2009 H1N1 pandemic.
Results suggest that 80% of the deaths occurred in people younger than 65 years, contrary to seasonal influenza where most deaths occur among the elderly.
Because the 2009 pandemic affected younger populations more than older populations, the global burden in terms of years of life lost was higher during this pandemic than it would be for a typical influenza season.
Additionally, the study suggests that 51% of the deaths may have occurred in south-east Asia and Africa, continents that are home to 38% of the world’s population, with the highest mortality rates occurring in Africa.
However, the authors warned that shortcomings in the availability of high-quality data for most countries affected by the pandemic could affect the accuracy of the new estimates.
Lead author Dr Fatimah Dawood of the US Government’s Centers for Disease Control and Prevention, 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 burden 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”.