Swine flu 15 times more deadly than thought, study claims

Many deaths from 2009 pandemic may have gone unreported in Asia and Africa. Photo / File

The swine flu pandemic of 2009 killed more than a quarter of a million people - 15 times more than the 18,500 reported, according to a paper in The Lancet Infectious Diseases journal.

The elevated toll from the H1N1 strain underlined the need for better planning and vaccine distribution, said researchers.

"This study is one of the first to provide a global estimate of deaths caused by the 2009 H1N1 virus," said lead author Fatimah Dawood of the US Centres for Disease Control and Prevention.

"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."

Some 18,500 deaths had been reported to the World Health Organisation from confirmed laboratory test results, but the international researchers believe this number to be a gross underestimation.

They wrote that "... diagnostic specimens are not always obtained from people who die with influenza and the viruses might no longer be detectable by the time of death in some people".

The team estimated there were 284,500 deaths from swine flu in the 12 months from April 2009. But the figure may be as high as 575,400, they said.

Between 250,000 and 500,000 people die of seasonal influenza every year, according to the WHO.

The first cases of H1N1 strain arrived in New Zealand on April 25, 2009, with students from Auckland's Rangitoto College returning from a trip to Mexico.

In the months that followed, the Ministry of Health reported more than 3500 cases of swine flu infection, and it was recorded as responsible for 20 deaths, although a dozen more may have resulted from infection.

In the 2009 flu season, H1N1 was the predominant virus, said Dr Dawood.

But comparing the numbers alone did not yield an accurate picture, she stressed, as 80 per cent of swine flu victims were younger than 65, while the yearly seasonal flu mainly tends to claim older victims.

The researchers said 51 per cent of swine flu deaths were estimated to have occurred in southeast Asia and Africa, which account for 38 per cent of the world's population.

The H1N1 virus affected some 214 countries and territories after it was uncovered in Mexico and the United States in April 2009. AAP