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Spanish flu poster (1918 and 2005)

It was the mother of all pandemics. In 1918, at the tail end of the First World War, a strain of influenza was to be unleashed on the human population, infecting some 500 million people worldwide and killing somewhere between 20 million and 50 million – many times more than the war itself.

No-one is sure where it started, although some have suspected the Far East, but it certainly wasn’t in Spain despite the name. This was merely the result of the fact that wartime censorship did not exist in Spain which meant that press reports of the pandemic’s progress there were not supressed, giving rise to the misguided notion that the outbreak actually started in Spain – hence the name “Spanish flu”. Interestingly, the Spanish themselves called it the Naples Soldier after a musical operetta called The Song of Forgetting in which a tune known as the Naples Solder was said to be as “catchy as the flu”.

The 1918 flu was unusual in that it proved deadliest for people aged between 20 and 40. Normally flu is most dangerous for the very young and the elderly. It also struck quickly. One anecdote from the time tells the story of four healthy women playing bridge into the night. By morning, three had died of the flu.

Doctors reported the “most viscous types of pneumonia” that they had ever seen, leaving people struggling for air. Others said patients were left struggling to clear their airways of blood-tinged froth that sometimes gushed from nose and mouth. Whether it was the profound virulence of the virus, or for another reason, the mortality rate ran at about 2.5 per cent compared to the typical 0.1 per cent death rate of typical influenza epidemics.

In 2005, scientists were able to reconstruct the H1N1 strain of the influenza virus that caused the 1918-19 pandemic as a result of isolating genetic fragments of the original virus retrieved from the frozen corpses of patients buried in the permafrost of the Arctic. It enabled scientists to study the genetic variation of the virus’s eight genes. One study based on this analysis even found a possible answer to why young, healthy adults were so vulnerable compared to the very young and very old. It was because their strong immune systems produced a cytokine storm, an overreaction of the immune system, that evidently proved fatal for so many within this particular age group.