A pandemic as severe as the 1918 Spanish flu could claim between 51 million and 81 million lives worldwide if it were to happen today, with most of those deaths occurring in the developing world, a study released Friday says.

The authors said such an event would more than double the number of deaths — from all causes —  that the entire world now experiences in a single year. And based on the patterns of 1918, they said 96 per cent or more of the lives lost would be in resource-poor countries.

"The evidence from 1918 is pretty impressive that in poor communities the death rate was just extraordinary. This is a remarkable increase in mortality in just a short period of time," said lead author Dr. Chris Murray, director of Harvard University's Initiative for Global Health.

The study, funded by the U.S. National Institute of Aging, will appear in Saturday's issue of The Lancet. Murray's co-authors are from Harvard, the University of Queensland, Australia and the Johns Hopkins Bloomberg School of Public Health in Baltimore.

The head of the World Health Organization's global influenza program admired the work, but said while it is an interesting exercise, it doesn't really change the task facing those working to prepare the world to weather a future pandemic.

"In terms of disease control and pandemic response and those sorts of thing, the bottom line is no matter what approach you take, the figures are pretty big and the steps needed to prepare for it are substantial," Dr. Keiji Fukuda said from Geneva.

Underestimating globalization

A U.S. infectious diseases expert challenged the paper's suggestion that the developed world would get off relatively lightly from a 1918-like pandemic, saying the study and an accompanying editorial underestimate the effect of globalization and overestimate the capacity of developed-world medical systems to cope with a crush of gravely ill people.

"The paper and the editorial have no sense at all of a modern global just-in-time economy, where the kind of drugs and medical services that they assume will be available in a modern world just won't be there," said Dr. Michael Osterholm, director of the Center for Infectious Diseases Research and Policy at the University of Minnesota.

But the author of the editorial, Dr. Neil Ferguson of Imperial College in London, supported the paper's assertion that the developing world would take a far bigger hit and contested Osterholm's prediction that supply chain disruptions would amplify the impact of a pandemic in developed countries.

"A pandemic is a relatively short-lived thing," said Ferguson, a leading mathematical modeller.

"There may be crises over a few weeks, but I would be skeptical whether we would face famine and the sort of food shortages and other problems that would lead to dramatically enhanced mortality. I just don't find it plausible."

Mortality estimates vary widely

Osterholm had earlier predicted a 1918-like pandemic could kill between 180 million and 360 million worldwide.

Those numbers, and others, are what inspired Murray and his colleagues to do this work. They had attended meetings of influenza experts where death projections were raised. The estimates varied wildly — from a low of two million to 360 million to even one billion people.

Murray said there seemed to be little scientific basis to those projections, so he and his colleagues set out to see if they could come up with an evidence-based estimate.

They hunted for death registries from the time, finding good records for 27 countries. In the case of India and the United States, they were even able to mine data from nine provinces and 24 states respectively.

In each case, they looked at nine years of deaths — the three years before 1918, the three years during the pandemic and the three after. They averaged the years before and after to come up with a standard death rate for that jurisdiction, then attributed any excess deaths that occurred in 1918-1920 to pandemic influenza.

They made exceptions for Britain and France to factor out the death toll of the First World War, and in Finland to account for a civil war that overlapped the end of the Spanish flu. Murray said similar adjustments were not made for Commonwealth countries like Canada, Australia and New Zealand that also fought in the First World War.

They then used the excess mortality rates — which varied from a low of 0.2 per cent in Denmark to a high of 7.8 per cent in parts of India — to calculate what a pandemic of similar virulence would do to the current global population.

Murray admitted he and his co-authors were startled by the projection they arrived at; they were expecting something more in the range of 10 million excess deaths.

He said the research points to a need to start looking for realistic ways cash-strapped countries can try to minimize the death toll, given that expensive antiviral drugs and scarce flu vaccine are likely to be unavailable except in the richest countries.