Flu: A warning from history
Experts believe that an infectious illness spreading around the world is not influenza.
Despite this, however, its virulent and contagious nature has already led to comparisons with the 1918 "Spanish Flu" pandemic.
The devastating 1918 pandemic is a reminder of the lethal nature of a handful of flu strains.
Every year, new versions of this common virus sweep from the Far East towards Europe, arriving for our traditional "flu season" between December and March.
Each year, based on reports of what is emerging elsewhere, experts in the UK formulate flu jabs to protect vulnerable groups here.
They have to do this every year because the virus is constantly mutating, presenting a new face to our immune systems.
However, most flu viruses, even those which make us ill, normally have at least a few familiar features which allow us to fight back.
Occasionally, however, the flu virus is so different in makeup that our immune system cannot muster any response.
These flu viruses are the most likely to kill even fit and healthy people.
These "novel viruses" crop up frequently, but it is those which are a combination of lethality and contagion which cause most concern.
A flu virus called "H5", which emerged in Hong Kong last year, killed 50% of all those it infected - fortunately it lacked a contagious nature, only affecting two people.
Professor Alan Hay, a WHO flu expert from the National Institute for Medical Research in London, told BBC News Online: "Although very few people were affected, H5 certainly set the alarm bells ringing."
The "perfect" combination virus is a rare event, but that is what happened in 1918, and again in 1957 and 1968.
The 1918 pandemic killed as many as 40 million, while the later outbreaks, while less serious, still claimed millions of victims.
Coming so hot on the heels of the Great War, the 1918 pandemic was the worst epidemic, at least in terms of numbers killed, in recorded history.
The bubonic plague of the 1300s killed fewer people - but came at a time of far lower populations.
The mortality rate was more than two in every hundred who caught the disease.
Killed within hours
It is possible that the mass movement of soldiers at the end of the conflict helped it spread around the globe.
Just like the latest virus, it is possible that the 1918 flu arose in China.
The illness came on swiftly, turning to a form of pneumonia that could kill within hours of the first symptoms becoming apparent.
Outbreaks swept through all the continents - in India, mortality was 50 deaths per 1,000 cases.
Experts warned that the increase in air travel from East to West meant that a new virus would take only a matter of days to circle the globe.
With cases of the new strain arising in Canada and Germany, it appears that they were right.
"Spanish Flu" is far from a footnote in history for scientists trying to protect us from future flu epidemics.
They even exhumed the bodies of flu victims buried in the permanently frozen ground of the Norwegian island of Spitzbergen, in the hope that traces of virus genetic material might have been preserved.
There is one thing that they agree on, however.
There has been no widespread "killer flu" outbreak since 1968, and they say that one is long overdue.
And there is no certainty that the medical world will be able to prevent its spread any better than in 1968.