It was the disease to end all others, infecting a third of humanity, killing tens of millions in their beds and prompting panicked talk of the end of days across continents still reeling from war.
One hundred years on from the influenza outbreak known as the Spanish Flu, scientists say that while lessons have been learned from the deadliest pandemic in history, the world is ill-prepared for the next global killer, according to AFP report.
In particular, they warn that shifting demographics, antibiotic resistance and climate change could all complicate any future outbreak.
"We now face new challenges including an ageing population, people living with underlying diseases including obesity and diabetes," University of Melbourne Dr Carolien van de Sandt, at the Peter Doherty Institute for Infection and Immunity, told AFP on Monday.
Scientists predict that the next influenza pandemic -- most likely to be a strain of bird flu that infects humans and spreads rapidly across the world via air travel -- could kill up to 150 million people.
Van de Sandt and her team examined reams of data on the Spanish Flu, which tore across the planet in 1918.
They also studied three further pandemics: the 1957 "Asian" flu, the "Hong Kong" flu of 1968 and 2009's swine flu outbreak.
They found that although the Spanish Flu infected one in three people, many patients managed to survive severe infection and others displayed only mild symptoms.
Unlike most nations, which used war-time censorship to supress news of the spreading virus, Spain remained neutral during World War I. Numerous reports of the sickness in Spanish media led many to assume the disease originated there and the name stuck.
It is now largely believed that the strain of flu in 1918 in fact originated among US servicemen and killed a disproportionately high amount of soldiers and young people, but researchers said things would be different this time around.
In 1918, in a world struggling with the economic impact of global war, the virus was rendered deadlier due to high rates of malnutrition.
But the team behind a new study, published in the Journal Frontiers in Cellular and Infection Microbiology, said the next outbreak will spread in the developed world among a population struggling with record obesity and diabetes rates.