World Death Toll Of a Flu Pandemic Would Be 62 Million
January 5, 2009
World Death Toll Of a Flu Pandemic Would Be 62 Million
Study Examined 1918-19 Outbreak
By David Brown
Washington Post Staff Writer
Friday, December 22, 2006; Page A03
An influenza pandemic of the type that ravaged the globe in 1918 and 1919 would kill about 62 million people today, with 96 percent of the deaths occurring in developing countries.
That is the conclusion of a study published yesterday in the Lancet medical journal, which uses mortality records kept by governments during the time of "Spanish flu" to predict the effect of a similarly virulent outbreak in the contemporary world.
The analysis, the first of its kind, found a nearly 40-fold difference in death rates between central India, the place with the highest recorded mortality, and Denmark, the country with the lowest. The reason for the huge variation is not known, but it may reflect differences in nutrition and crowding.
If a modern Spanish flu killed all its victims in one year, it would more than double global mortality. About 59 million people now die each year.
"It is a huge, huge number," said Christopher J.L. Murray, a physician and biostatistician at the Harvard School of Public Health who headed the study. "This really took us by surprise."
One of the World Health Organization's key influenza experts, however, called the main public health implication of the study "no surprise."
"The countries most likely to be adversely affected are the ones with the least resources. This happened then, and is what is likely to happen now," said Keiji Fukuda. "WHO, as it always has done, pays a disproportionate amount of its attention and efforts toward such countries."
Historical accounts suggest that what became known as Spanish flu emerged at an Army camp in Kansas in early March 1918. It was carried to Europe by American troops, where it circulated before undergoing a change early the next fall that made it unusually lethal. It spread around the world and was brought back to the United States, where it killed hundreds of thousands of Americans in October and November 1919. It circulated until early 1920, with virtually everyone on Earth eventually exposed to the virus.
The global death toll from the pandemic is unknown. In the 1920s, it was estimated to be about 20 million. A more complete analysis in 1991 raised that to 30 million. One in 2002 said mortality "may fall in the range of 50 to 100 million."
The new study doesn't make a new estimate. Instead, it calculated the death rate in places that had good birth and death records in 1918 and 1919 in order to estimate what would happen in a larger, older and relatively more affluent world population nearly a century later.
The places with good records included most European nations, the United States, Canada, Australia, Japan and several Latin American countries. The keys to the project, however, were accurate death registries in India, Sri Lanka, Taiwan and the Philippines. They allowed Murray and his colleagues to estimate what happened among the world's non-European poor, where eyewitness accounts describe huge mortality, but few reliable statistics existed.
By far the most informative data came from India.
"The British colonial administration -- they were very good record-keepers," said Murray, who noted that India's contemporary death registries are less complete than ones from 1918.
The researchers compared the death rates during the 1918-1920 period with those in the three years before and after the pandemic. This gave an estimate of "excess mortality" during the flu years, which was assumed to be caused directly or indirectly by the virus. (Because men in countries fighting in World War I had elevated mortality in 1918, they were excluded from the calculation.) The extra deaths ranged from 0.2 percent of the population in Denmark to 7.8 percent in the Central Provinces and Berar region of India -- a 39-fold difference.
In the United States, they ranged from a low of 0.25 percent in Wisconsin to 1 percent in Colorado. (The best-known work of fiction about the pandemic, "Pale Horse, Pale Rider," is Katherine Anne Porter's account of her near-death experience during the Colorado outbreak.) Flu death rates varied greatly over short distances. Virginia's excess mortality, 0.47 percent, was well below Maryland's, 0.72 percent. Sweden's (0.66 percent) was three times Denmark's (0.2 percent).
Murray and his colleagues analyzed the death patterns and deduced that about half the variation from region to region was explained by differences in per capita income. For every 10 percent increase in income, a person's risk of dying during the pandemic fell 10 percent.
Why the poor were so vulnerable is unknown. It could have been that many were already ill with parasites or other illnesses or lacked micronutrients such as Vitamin A and zinc that are essential to immunity.
To estimate the effects of a modern Spanish flu, the researchers applied the 1918-1920 death rates to the current world population broken down by income, sex and age. They came up with a range of 51 million to 81 million deaths, with a median of 62 million.
Even though the world's population is three times what it was during the Spanish flu pandemic, the estimated mortality of a modern Spanish flu isn't three times what it was in 1918. That is mainly because per capita income is higher now -- and the higher the income, the lower the risk of dying of influenza.
The illness caused by the 1918 virus was largely untreatable. There were no antiviral drugs, no mechanical ventilators to help people breathe and no antibiotics to treat bacterial pneumonias that often set in after the viral infection. All are available now and would reduce the death toll, though some interventions would be in sort supply during a pandemic.
Flu pandemic could kill up to 81 million people
Deadly virus would have 'devastating impact' worldwide, new study finds
The Associated Press
Updated: 4:13 p.m. PT Dec 21, 2006
LONDON - A flu virus as deadly as the one that caused the 1918 Spanish flu could kill as many as 81 million worldwide if it struck today, 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 did 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,” Murray said. “It turns out we were wrong.”
The new work is published in Saturday’s issue of the journal The Lancet.
The 1918 flu outbreak killed at least 40 million people worldwide. But flu pandemics have varied widely in their severity. The most recent, in 1957 and 1968, were relatively mild, killing 2 million and 1 million people worldwide respectively.
To get their estimates, Murray and his 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 compared death rates during the pandemic to average death rates before and after. 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 worldwide would more than double, jumping by 114 percent.
Developing countries hardest-hit
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 makeup of the virus that will cause deaths, but that there are a lot of other things that intervene,” he said.
Determining the mitigating factors might help avert a catastrophe. “If we can answer that question, we may unlock the mysteries behind which non-pharmaceutical strategies could significantly decrease mortality,” said Murray.
Population density, nutrition and immune status could all play roles, he suggests.
“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 the World Health Organization’s Global Influenza Program. “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 rose, with circulation of the H5N1 bird flu virus on a large scale in late 2003, the global community has 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 advances remain out of reach for poor countries.
'A devastating impact'
Another question is the impact a flu pandemic would have on those infected with HIV. Seasonal influenza exacts a heavy toll on those with weakened immune systems. So, in the case of a new pandemic flu, Murray’s estimate might be optimistic.
And while the Spanish flu often has been regarded as a worst-case scenario, there is no guarantee 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 2 percent. The fatality rate for the H5N1 virus is about 60 percent.
However, experts think that if H5N1 were to evolve into a strain easily transmissible between people, it would also become less deadly.
“It’s not in a virus’ interest to kill its hosts so readily, otherwise it can’t reproduce,” said Dr. Ian Gust, a flu expert at the University of Melbourne, Australia.
Still, there is no guarantee that H5N1 would become less deadly.
If it doesn’t, “we would be in for a devastating impact,” said Gust. “All bets would be off.”
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Has anyone counted / identified / described the number of characteristics where H5N1 differs with the 1918 virus?
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