Spanish flu was treated at first as a bit of a joke. Nobody in May 1918 had the faintest idea it would end up killing more people than any other pandemic in human history.

As a recent survey of the literature says,

“Because of the initial perceived lack of severity of the illness and because of the Spanish sense of humour, the influenza was known popularly in Madrid as the ‘Soldado de Napoles’ (‘Naples Soldier’), which was the name of a popular song from a highly successful musical, La canción del olvido, which was playing at the same time at Madrid’s Teatro de la Zarzuela. The song was so popular that it was deemed to be ‘highly contagious’, like influenza.”

The authors of the survey end by urging the world to “never forget the warning” posed by Spanish flu. But one lesson of this earlier pandemic is that it can be strangely difficult, either while the disease is taking hold or even with the benefit of hindsight, to establish what is going on.

Nobody knows how many people were killed by Spanish flu. The estimates range from 50 million to 100 million. In Britain about 250,000 people died, in France 400,000, in the United States over 500,000, in Iran between 900,000 and 2,400,000, in China between one and nine million, in India perhaps 17 million.

One’s senses are soon numbed by such statistics. From August 1918, the disease took on a new, more lethal form, but none of the powers fighting the First World War, which continued until 11th November, wished to admit being weakened by it.

The British Prime Minister, David Lloyd George, went down with Spanish flu on 12th September 1918, the day he received the freedom of the city of Manchester, where he had been born.

He was too ill to be moved, so for ten days was treated in a committee room in Manchester Town Hall, breathing with the help of a respirator, which he also required on the journey back to London. The severity of his condition, which was “touch and go” according to his valet, was concealed from the public, and in due course he made a full recovery.

We are inclined to expect medical science to be exact. The doctor will tell us what the matter is. But very often, no clear answer is forthcoming.

And this is true on a colossal scale with Spanish flu. To this day, it is not clear where the disease started, but it was certainly not in Spain.

As a neutral power, Spain had no need to hush up the epidemic, especially as it seemed at first, though highly contagious, not very dangerous. The case of the Spanish King, Alfonso XIII, was widely reported in the foreign press. He recovered, but the illness became known as Spanish flu.

According to The National Geographic, Spanish flu may have originated in China:

“Historian Mark Humphries of Canada’s Memorial University of Newfoundland says that newly unearthed records confirm that one of the side stories of the war—the mobilization of 96,000 Chinese labourers to work behind the British and French lines on World War I’s Western Front—may have been the source of the pandemic.”

American scientists are inclined to trace the outbreak to Camp Funston, at Fort Riley in Kansas, where large drafts of troops assembled prior to departure for Europe, and where there was certainly an outbreak in March 1918 of a disease that was at least similar to Spanish flu,

But as Mark Honigsbaum, author of Living With Enza: The Forgotten Story of Britain and the Great Flu Pandemic of 1918, wrote in a hundredth anniversary piece for The Guardian:

“A rival theory, favoured by the British virologist John Oxford, is that the pandemic began at Etaples, a huge British military camp an hour south-west of Boulogne. With accommodation for up to 100,000 soldiers, Etaples lay on a migratory bird flyway close to the Somme estuary and had all the necessary conditions for a spillover event: wild waterfowl, plus chickens and pigs, living in close proximity to men packed into airless barracks. Etaples also had several hospitals where soldiers whose lungs had been compromised by mutagenic gases deployed on the battlefield were evacuated for treatment.

“In the winter of 1917, several hundred British soldiers collapsed with influenza-like symptoms and medics at Etaples recorded 156 deaths. At the time, the epidemic was labelled ‘purulent bronchitis’ because of the yellow pus that oozed from the larger airways of the lungs at autopsy (some medics thought it resembled the lung damage from phosgene gas).

“Another prominent feature was cyanosis, a distinctive purple-blue discolouration of the lips, ears and cheeks, caused by the loss of oxygen to the heart. Cyanosis was also a hallmark of the pneumonias associated with the Spanish flu – an observation that persuaded doctors writing in the Lancet in 1919 that it and purulent bronchitis had been ‘fundamentally the same condition’.”

My great-grandfather, Alexander Ogilvie, was gassed on the Western Front shortly before the end of the First World War, and evacuated, most likely via Etaples, blinded and unconscious to England, where he died of pneumonia on 30th October 1918.

A curious feature of Spanish flu was that unlike other versions of the disease, which are most deadly for the old and for small children, it posed the greatest threat to healthy adults aged between 20 and 40.

It is possible that older people had acquired a degree of immunity thanks to having caught earlier versions of flu. It is also possible that Spanish flu provoked an over-reaction of the immune system, known as a cytokine storm, so the stronger your immune system was, the worse the effects.

Yet another curiosity of Spanish flu is that it was at its most deadly in late summer and autumn, whereas winter is usually the worst time for flu.

The head reels at so much uncertainty. Spanish flu defies understanding, and came to be seen as a sad but indistinct event about which not much needed to be said, compared to the endless studies of the actual fighting.

No wonder the experts cannot tell us what will happen with the coronavirus, but are profoundly worried about what could happen. The NHS issues studiously calm advice about avoiding contact with other people if you have returned from Wuhan or Hubai Province in China in the last 14 days, and  we wait to see how well the condition can be contained.