Posted: Sat Dec 23, 2006 10:56 am
Flu virus 'could kill 81 million'
December 22, 2006
LONDON, England (AP) -- If a flu virus as deadly as the one that caused 1918 Spanish flu struck today, it could kill as many as 81 million worldwide, a new study estimates.
By applying historical death rates to modern population data, the researchers calculated a death toll of 51 million to 81 million, with a median estimate of 62 million.
That's surprisingly high, said lead researcher Chris Murray of Harvard University. He'd done the analysis in part because he thought prior claims of 50 million deaths were wildly inflated.
"We expected to end up with a number between 15 and 20 million," said Murray. "It turns out we were wrong."
The new work is published in Saturday's issue of the journal The Lancet.
The 1918 outbreak killed at least 40 million people worldwide. But flu pandemics have varied widely in their severity. The last two, in 1957 and 1968, were relatively mild, killing two million and one million people worldwide respectively.
Many numbers have been tossed out in speculating how many people might die in the next flu pandemic, ranging from several million to several hundreds of millions, but the guessing game will continue until the actual pandemic strain emerges.
To get their estimates, Murray and colleagues examined all available death registration data from 1914 to 1923. There was sufficient information from 27 countries, including numbers from 24 U.S. states and nine provinces in India.
The researchers then compared death rates during the pandemic to average death rates beforehand and afterward. That revealed how much the pandemic flu contributed to death rates, a figure called excess mortality. They then applied the excess mortality data to worldwide population data from 2004.
If their median estimate of 62 million flu deaths occurred in a single year, the total number of deaths from all causes around the world would more than double, jumping by 114 percent.
One surprise in the new study was the huge variation in how different countries would be affected by a pandemic. The study estimates that 96 percent of the deaths would occur in the developing world. Murray and colleagues noted there was a 30-fold or more variation in mortality.
"That tells us it's not just the genetic make-up of the virus that will cause deaths, but that there are a lot of other things that intervene," he said.
Determining what some of these mitigating factors are might help to avert a similar catastrophe in the future. "If we can answer that question, we may unlock the mysteries behind which non-pharmaceutical strategies could significantly decrease mortality," said Murray. Issues such as population density, nutritional or immune status could all play a role, he suggests.
Some experts warn that planning based on the Spanish flu -- the deadliest infectious disease event ever recorded -- is skewed. The World Health Organization estimates that in a moderate pandemic, based on the 1957 and 1968 pandemics, up to 7.4 million people might die.
"We know that even if we have much lower numbers of deaths worldwide than in 1918, the world will be severely stressed," said Dr. Keiji Fukuda, coordinator of WHO's Global Influenza Programme. "Speculating about the possible numbers is an interesting exercise, but the really important thing is, what do we do about it?"
Since the pandemic threat first arose, with the circulation of the H5N1 bird flu virus on a large scale in late 2003, the global community has greatly bolstered its pandemic preparedness plans.
Medical systems today are far stronger than they were last century, and the availability of antivirals and antibiotics -- which did not exist in 1918 -- should help greatly.
Still, many of these advantages remain out of reach for poor countries. A big question mark also looms over the impact a flu pandemic would have on the approximately 35 million people infected with HIV. Seasonal influenza exacts a heavy toll on people with weak immune systems, thus, in the case of a new pandemic flu, Murray's estimate might even be optimistic.
And while the Spanish flu has often been regarded as a worst-case scenario, there is no guarantee that the next pandemic will not be even more deadly. Despite the tens of millions of deaths the 1918 flu caused, the death rate among those infected was approximately two percent.
In comparison, the fatality rate for the H5N1 virus, currently thought to be the most likely candidate to spark a flu pandemic hovers around 60 percent.
But experts think that if H5N1 were to evolve into a strain easily transmissible between people, it would have to trade some of its lethality for transmissibility.
"It's not in a virus' interest to kill its hosts so readily, otherwise it can't reproduce itself," said Dr. Ian Gust, a flu expert at the University of Melbourne, Australia.
There is no guarantee, however, that H5N1 will make such a concession if it does ultimately ignite the next pandemic.
"If that happens, we would be in for a devastating impact," said Gust. "All bets would be off."
December 22, 2006
LONDON, England (AP) -- If a flu virus as deadly as the one that caused 1918 Spanish flu struck today, it could kill as many as 81 million worldwide, a new study estimates.
By applying historical death rates to modern population data, the researchers calculated a death toll of 51 million to 81 million, with a median estimate of 62 million.
That's surprisingly high, said lead researcher Chris Murray of Harvard University. He'd done the analysis in part because he thought prior claims of 50 million deaths were wildly inflated.
"We expected to end up with a number between 15 and 20 million," said Murray. "It turns out we were wrong."
The new work is published in Saturday's issue of the journal The Lancet.
The 1918 outbreak killed at least 40 million people worldwide. But flu pandemics have varied widely in their severity. The last two, in 1957 and 1968, were relatively mild, killing two million and one million people worldwide respectively.
Many numbers have been tossed out in speculating how many people might die in the next flu pandemic, ranging from several million to several hundreds of millions, but the guessing game will continue until the actual pandemic strain emerges.
To get their estimates, Murray and colleagues examined all available death registration data from 1914 to 1923. There was sufficient information from 27 countries, including numbers from 24 U.S. states and nine provinces in India.
The researchers then compared death rates during the pandemic to average death rates beforehand and afterward. That revealed how much the pandemic flu contributed to death rates, a figure called excess mortality. They then applied the excess mortality data to worldwide population data from 2004.
If their median estimate of 62 million flu deaths occurred in a single year, the total number of deaths from all causes around the world would more than double, jumping by 114 percent.
One surprise in the new study was the huge variation in how different countries would be affected by a pandemic. The study estimates that 96 percent of the deaths would occur in the developing world. Murray and colleagues noted there was a 30-fold or more variation in mortality.
"That tells us it's not just the genetic make-up of the virus that will cause deaths, but that there are a lot of other things that intervene," he said.
Determining what some of these mitigating factors are might help to avert a similar catastrophe in the future. "If we can answer that question, we may unlock the mysteries behind which non-pharmaceutical strategies could significantly decrease mortality," said Murray. Issues such as population density, nutritional or immune status could all play a role, he suggests.
Some experts warn that planning based on the Spanish flu -- the deadliest infectious disease event ever recorded -- is skewed. The World Health Organization estimates that in a moderate pandemic, based on the 1957 and 1968 pandemics, up to 7.4 million people might die.
"We know that even if we have much lower numbers of deaths worldwide than in 1918, the world will be severely stressed," said Dr. Keiji Fukuda, coordinator of WHO's Global Influenza Programme. "Speculating about the possible numbers is an interesting exercise, but the really important thing is, what do we do about it?"
Since the pandemic threat first arose, with the circulation of the H5N1 bird flu virus on a large scale in late 2003, the global community has greatly bolstered its pandemic preparedness plans.
Medical systems today are far stronger than they were last century, and the availability of antivirals and antibiotics -- which did not exist in 1918 -- should help greatly.
Still, many of these advantages remain out of reach for poor countries. A big question mark also looms over the impact a flu pandemic would have on the approximately 35 million people infected with HIV. Seasonal influenza exacts a heavy toll on people with weak immune systems, thus, in the case of a new pandemic flu, Murray's estimate might even be optimistic.
And while the Spanish flu has often been regarded as a worst-case scenario, there is no guarantee that the next pandemic will not be even more deadly. Despite the tens of millions of deaths the 1918 flu caused, the death rate among those infected was approximately two percent.
In comparison, the fatality rate for the H5N1 virus, currently thought to be the most likely candidate to spark a flu pandemic hovers around 60 percent.
But experts think that if H5N1 were to evolve into a strain easily transmissible between people, it would have to trade some of its lethality for transmissibility.
"It's not in a virus' interest to kill its hosts so readily, otherwise it can't reproduce itself," said Dr. Ian Gust, a flu expert at the University of Melbourne, Australia.
There is no guarantee, however, that H5N1 will make such a concession if it does ultimately ignite the next pandemic.
"If that happens, we would be in for a devastating impact," said Gust. "All bets would be off."