Health officials warn that millions could die in a flu pandemic. It would not be the first time. The Spanish flu virus that swept the world in 1918-19 is considered one of the most deadly diseases in history.
Spanish flu patients crowd an emergency hospital in Kansas
In March 1918 an army cook reported to the infirmary at Fort Riley, Kansas, with a temperature of 39.5 C.
Within two days a further 521 men had been taken sick, in what is thought to have been one of the first recorded outbreaks of what came to be known as Spanish flu.
Striking a world already devastated by war, such early warning signs were largely missed and the influenza went on to kill 40 million in a matter of months.
Scientists now believe the virus came from birds and that it bore similarities to the avian flu at the centre of the current scare.
After travelling back and forth between the US and Europe with troops, who were among the worst affected, the virus soon reached Africa and Asia.
August brought the second wave of the virus, with "explosive" outbreaks in France, Sierra Leone and the US and a 10-fold increase in deaths, says the World Health Organization.
The virus quickly spread, with few communities untouched and between 25% and 30% of the world population infected.
So unfamiliar was Spanish flu that many doctors suspected an outbreak of meningitis, or even a return of the Black Death.
"The disease had features that were not seen before and, fortunately, have not been seen since," says the WHO.
Unlike most deaths from influenza, the majority of victims were neither the young or old, but those between 15 and 35. As many as 99% were under 65.
Many deaths were from pneumonia caused by secondary infections, but others died from a haemorrhaging of the lungs. Other symptoms included a blue tinge to the skin.
One doctor at a US Army camp near Boston wrote in September 1918 that men coming in with what appeared to be ordinary influenza quickly worsened.
"It is only a matter of a few hours until death comes, and it is simply a struggle for air until they suffocate," says the letter, obtained by Stanford University.
"It is horrible. One can stand it to see one, two or twenty men die, but to see these poor devils dropping like flies sort of gets on your nerves."
In many countries schools were closed, public gatherings banned and people encouraged to wear masks.
SPANISH FLU DEATHS 1918-19
India - 10 to 17 million
Sub-Saharan Africa - 1.5 to 2 million
US - 500,000 to 675,000
France - 400,000
UK - 250,000
All figures estimates
In some cases those caught sneezing or coughing unprotected in public were fined or imprisoned and one US town outlawed shaking hands.
The efforts failed - as did the widespread practices of quarantine and isolation.
In India more than 10 million died, while up to two million were killed in sub-Saharan Africa.
Some estimates suggest that in Spain up to eight million people were infected, the country's papers' in-depth coverage of the outbreak prompting the "Spanish flu" name.
But like other pandemics, the outbreak ended as quickly as it started.
By the time it reached Australia in early 1919, the virus had taken on a milder form and while there were still deaths, the worst was over.