The Next Pandemic

It is the nature of the influenza virus to cause pandemics. There have been at least 11 in the last 300 years, and there will certainly be another one, and one after that, and another after that. And it is impossible to predict whether a pandemic will be mild or lethal.

In 1997 in Hong Kong, the H5N1 virus jumped directly from chickens to 18 people, killing six. Public health officials slaughtered hundreds of thousands of ducks, chickens and other fowl to prevent further spread, and the virus seemed contained. It wasn't. In 2004, H5N1 returned with a vengeance. Since then, it has killed hundreds of millions of birds, while several hundred million more have been culled in prevention efforts. And it has infected more than 500 human beings, killing 60 percent of those infected. The virus's high mortality rate and memories of the 1918 influenza—the best estimates of that death toll range from 35 to 100 million people—got the world's attention. Every developed nation prepared for a pandemic, as did local and regional governments and the private sector. They all based their preparations on a 1918-like scenario, but it did not come. It still could.

In March 2009, another influenza pandemic caused by a different virus did arrive, and it was nothing like the lethal one we expected. This particular H1N1 virus generated a pandemic with the lowest case mortality rate of any known outbreak in history. Nothing the world did accounted for the low death toll; it was simply luck that this pandemic virus had low lethality. The World Health Organization counts fewer than 20,000 dead worldwide, but that's only laboratory-confirmed cases. It is impossible to know whether actual mortality was 10 or even 100 times that number.

But even the highest reasonable estimate of those killed by this latest pandemic so far—we could still see more waves of infection—still falls far below the anticipated scenario. The world assumed that preparing for a severe pandemic would allow it to adjust easily to a mild one. It was mistaken. This lesser pandemic threw the world off-balance, and very few nations have, with respect to influenza, regained their footing.

A World Under Pressure

The 2009 pandemic put the world under pressure and revealed flaws in both health systems and, more significantly, in international relations. The lessons we might learn from this past event could be of value in our ongoing war against the flu virus. But we're still getting too many things wrong.

Virologists, epidemiologists, public health officials, even ethicists and logisticians are analyzing data from the pandemic. Based on their results, health organizations will likely adopt modest management changes. The WHO previously defined an influenza pandemic as basically any occurrence in which a new influenza virus enters the human population and passes easily between humans; it may refine that definition by adding a virulence factor, similar to the Saffir-Simpson scale for hurricanes (category 1 to category 5). Vaccine delivery systems will improve. Local hospitals will upgrade their triage practices. And some fundamental changes which were already underway—such as shifting vaccine production away from chicken eggs, a technology used for more than half a century, to new production technologies—will accelerate.

These are good starting points. But on larger policy and scientific questions any efforts to draw conclusions could mislead. All other pandemics we know about in any detail—in 1918, 1957 and 1968—sickened 25 percent of the population or more in every country for which data exists. The 2009 data suggests attack rates approached that benchmark figure in children only, while adults were generally attacked at only a quarter to a half that rate, not because of any public health measures taken but most likely because adults had already been exposed to a similar virus and had some immunity. This distinctly unusual pattern makes it difficult to draw conclusions on the effectiveness of, for example, such non-pharmaceutical interventions as screening airport arrivals or shutting down schools. Yet some epidemiologists are insisting on doing just that. Policy for the next pandemic is being...