As their lungs filled … the patients became short of breath and increasingly cyanotic. After gasping for several hours they became delirious and incontinent, and many died struggling to clear their airways of a blood-tinged froth that sometimes gushed from their nose and mouth. It was a dreadful business.

--Isaac Starr, 3rd year medical student, University of Pennsylvania, 1918.

By the fall of 1918 a strain of influenza seemingly no different from that of previous years suddenly turned so deadly, and engendered such a state of panic and chaos in communities across the globe, that many people believed the world was coming to an end. It struck with amazing speed, often killing its victims within just hours of the first signs of infection. So fast did the 1918 strain overwhelm the body's natural defenses, that the usual cause of death in influenza patients---a secondary infection of lethal pneumonia---oftentimes never had a chance to establish itself. Instead, the virus caused an uncontrollable hemorrhaging that filled the lungs, and patients would drown in their own body fluids.

Not only was the Spanish Flu strikingly virulent, but it displayed an unusual preference in its choice of victims---tending to select young healthy adults over those with weakened immune systems, as in the very young, the very old, and the infirm. The normal age distribution for flu mortality was completely reversed, and had the effect of gouging from society's infrastructure the bulk of those responsible for its day to day maintenance. No wonder people thought the social order was breaking down. It very nearly did.

But at the close of the First World War, when Spanish Flu appeared, the world was a very different place. Since then, outstanding advances in our knowledge of the germ world have been made, adding dramatically to our repertoire of medical wizardry. Surely what happened back then couldn't happen again.

Or could it?

During the 1918-1919 fall period the number of Americans who died from influenza is estimated at 675,000. Of those, almost 200,000 deaths were recorded in the month of October 1918 alone. Worldwide, the mortality figure for the full pandemic is believed to stand somewhere between 30 to 40 million. So, with the world population today having more than tripled in the intervening years, what is to stop a modern flu pandemic from claiming upwards of 100 million lives? The answer, it seems, is nothing at all.

Today, of course, we have vaccines and antiviral drugs. But in the Third World, at least, these combatants are in very short supply. In India, where the Spanish Flu is thought to have culled more than 10 million from the population, public health care is still notoriously deficient. In China, with a population one third larger again, the situation is not much better. Even for developed countries, where vaccines are readily available, the fraction of the population that routinely subjects itself to inoculation generally hovers around 10 percent. In the event that the public were to receive adequate warnings of an impending pandemic, it's likely of course that this number could be significantly increased. But even then, it may not matter. By their nature pandemics tend to take us by surprise. The next influenza strain that ravages the human population will probably not be the one we were planning to encounter.

If all this seems a little alarmist in nature, consider for a moment the recent controversy surrounding what Robert Webster, chairman of the Department of Virology and Molecular Biology at Saint Jude Children's Research Hospital in Memphis, Tennessee, has called The Hong Kong Incident.

In 1997 epidemiologists and public health officials from around the world got their first glimpse¹ of an entirely new variety of human influenza. Known as subtype H5N1 for the surface proteins which the virus carries, the new strain had only ever previously been observed in birds. Ominously, the effect of H5N1 on poultry had earned it the evocative title of "Chicken Ebola." And when it surfaced in the human population of Hong Kong last year it proved to be almost as deadly.

How deadly? Even with the advantages of intensive-care treatment, fully one third of the first 18 confirmed cases never recovered. They died. The numbers are suggestive of the death tolls suffered by immunologically-isolated Alaskan villages in 1918, where, in some cases, half the population was lost to the disease. In Hong Kong, bird-to-human contact is believed to have been the transmission route. Fearing a public health crisis, city officials in December of 1997 ordered the slaughter of Hong Kong's entire poultry population. All ducks, geese, and chickens in the city were killed. Fortunately it appears the H5N1 subtype lacks the ability to transmit itself through the air from one human host to the next potential victim.

On the surface, HK97 shows the hallmarks of what might be described as a "near miss" for our species. In other words, a biological catastrophe. Or it could be a false alarm. It's too early to say. Either way, it's hard to argue that we didn't just receive a wake-up call of sorts. Maybe what happened in 1918 has today merely the substance of a tenuous memory, but it also marks a lesson that clearly would be dangerous to forget. On the scale of a human life span, pandemic influenza is a rarity, but no-one seriously doubts that it will be back.

As Webster reminds² us, "All the genes of all influenza viruses in the world are being maintained in aquatic birds, and periodically they transmit to other species... The 1918 viruses are still being maintained in the bird reservoir. So even though these viruses are very ancient, they still have the capacity to evolve, to acquire new genes, new hosts. The potential is still there for the catastrophe of 1918 to happen again."