On 28 September 1918, a Spanish newspaper gave its readers a short lesson on influenza. “The agent responsible for this infection,” it explained, “is the Pfeiffer’s bacillus, which is extremely tiny and visible only by means of a microscope.”


The explanation was timely, because the world was in the grip of the most vicious flu pandemic on record – but it was also wrong: flu is caused by a virus. Unfortunately, it wasn’t just one Spanish newspaper that had misidentified the causative agent of the disease. The idea that flu was caused by a bacillus, or bacterium, was accepted by the most eminent scientists of the day, who would find themselves almost entirely helpless in the face of the scourge.

How many people died from the Spanish flu?

The Spanish flu was one of the deadliest disasters in history. It lasted for two years – between the first recorded case in March 1918 and the last in March 1920, an estimated 50 million people died, though some experts suggest that the total might actually have been twice that number.

The ‘Spanish flu’ killed more than the First World War, possibly more even than the Second World War – indeed, perhaps more than both put together.

How does Spanish flu compare to Coronavirus? In our recent podcast, Laura Spinney told us: “You might have seen a figure floating around of a case fatality rate of 3.4%, which refers to the proportion of people who catch the Covid-19 infection who go on to die of it. The number that’s often quoted for the Spanish Flu, for example, case fatality rate is 2.5% but it’s a very, very, very controversial figure because the numbers are so vague. I mean, we think that probably 50 million people died but there was no form of reliable test at the time so we can’t be sure about that and that just throws all the numbers out. “So it’s really difficult to make the historical comparisons, even if you have accurate data now, which we don’t. So on both sides of the equation, if you like, it’s a moving target. “We would obviously love to have a vaccine against Covid-19 now but we don’t and we may have to wait a year to 18 months for that. They had no vaccine at all in 1918. Or rather, they did make vaccines but they were useless, pretty much, because they were essentially vaccines against bacteria in the respiratory tract whereas, as we know, flu is a viral disease. “So in terms of that, we are much advanced compared to 1918. But we don’t have that vaccine yet. We so have anti-viral drugs for treating the sick and we do have antibiotics which will be useful for treating the bacterial complications that may cause pneumonia in some cases, as they did also in 1918, interestingly.” Read a transcript of the podcast here

The pandemic struck at a critical juncture in the evolution of understanding of infectious disease. Well into the 19th century, epidemics were considered acts of god – a notion that dated back to the Middle Ages. Bacteria were first observed in the 17th century, but initially weren’t connected with human illnesses. In the late 1850s the French biologist Louis Pasteur made the connection between micro-organisms and disease, and from a couple of decades later German microbiologist Robert Koch furthered modern concepts of infectious disease. ‘Germ theory’ was disseminated far and wide, slowly replacing more fatalistic ideas.

By the 20th century the application of germ theory, combined with improvements in hygiene and sanitation, had made significant inroads against the so-called ‘crowd’ diseases that afflicted human communities, especially those inhabiting the great cities that had mushroomed in the wake of the industrial revolution. Throughout the 19th century, so many urbanites had been lost to such diseases – cholera, typhus and tuberculosis, to name but three – that cities needed a steady influx of healthy peasants from the countryside to keep up their numbers. Now, at last, they had become self-sustaining.

Where did the Spanish flu originate? One of the few certainties we have about the Spanish Flu Pandemic is that it didn’t start in Spain. We actually don’t know where it did start – but we know it didn’t start in Spain. The Spanish felt, and to a very great degree were, stigmatised by this. There is also no way of being certain where Spanish Flu originated, although the trenches of the First World War, where poor sanitation and disease was rife, are an often-cited contender. The filthy, rat-infested conditions undoubtedly affected the soldiers’ immune systems, making them more vulnerable to illness. It is thought the first cases were in military forts in the United States before spreading at an alarming rate to Europe. But yet the pandemic was called ‘Spanish Flu’ – again, a result of the war. Why was Spanish Flu called Spanish flu? Wartime censorship exaggerated the affects of the virus in Spain. While Britain, France, Germany and the United States censored and restricted early reports, papers in Spain – as a neutral country – were free to convey all the horrid details of the pandemic. This made it look much worse there, so the unfortunate name spread with the disease around the world.

By 1918, then, faith in science was high, and some scientists had even adopted a certain swagger. Twelve years earlier, this had prompted the Irish playwright George Bernard Shaw to write The Doctor’s Dilemma, in which an eminent doctor, Sir Colenso Ridgeon – a character based on Sir Almroth Wright, who developed the typhoid vaccine – plays god with his patients’ destinies. Shaw was warning doctors against hubris, but it took an outbreak of another ‘crowd’ disease – influenza – to bring home to them just how little they knew.

When scientists thought about ‘germs’ in the early 20th century, they generally thought about bacteria. The virus was a novel concept; the first virus, discovered in 1892, infected tobacco plants and had been detected indirectly by its ability to transmit disease. Unlike many bacteria, it was too small to be seen through an optical microscope. Without having actually seen viruses, scientists debated their nature: were they organism or toxin, liquid or particle, dead or alive? They were veiled in mystery, and nobody suspected that they could be the cause of flu.

During the previous flu pandemic – the so-called ‘Russian’ flu, which began in 1889 – a student of Koch’s named Richard Pfeiffer claimed to have identified the bacterium that caused the flu. Pfeiffer’s bacillus, as it became known, does exist and does cause disease – but it does not cause flu. During the 1918 pandemic, pathologists who cultivated bacterial colonies from the lung tissue of flu victims found Pfeiffer’s bacillus in some, but not all, of their cultures, and this puzzled them. To add to doctors’ puzzlement, vaccines created against Pfeiffer’s bacillus seemed to benefit some patients. In fact, these vaccines were effective against secondary bacterial infections that caused pneumonia – the ultimate cause of death in many cases – but scientists didn’t know that at the time. They would realise their mistake too late.

Why was it called ‘Spanish flu’?

The Russian flu had acquired its name because it was thought to have originated in Bukhara in Uzbekistan (at that time, part of the Russian empire). The pandemic that broke out nearly 30 years later will always be known as the ‘Spanish flu’, though it didn’t start in Spain.

It washed over the world in three waves which, in the northern hemisphere, corresponded to a mild wave in the spring of 1918, a lethal wave the following autumn, and a reprisal in the early months of 1919 that was intermediate in virulence between the other two. The first cases were officially recorded in March 1918 at Camp Funston, a military base in Kansas. Within six weeks the disease had reached the trenches of the western front in France, but it wasn’t until May that the flu broke out in Spain.

Unlike the United States and France, Spain was neutral in the war, so it didn’t censor its press. The first Spanish cases were therefore reported in the newspapers, and because King Alfonso XIII, the prime minister and several members of the cabinet were among those early cases, the country’s plight was highly visible. People all over the world believed that the disease had rippled out from Madrid – a misconception encouraged by propagandists in those belligerent nations that knew they’d contracted it before Spain. In the interests of keeping morale high in their own populations, they were happy to shift the blame. The name stuck.

Understandably, Spaniards smarted at this calumny: they knew they were not responsible, and strongly suspected the French of having sent the flu across the border, but they couldn’t be sure. They cast around for a different label, and found inspiration in an operetta performed at the capital’s Zarzuela Theatre – a hugely popular reworking of the myth of Don Juan, featuring a catchy tune called ‘The Soldier of Naples’. The catchy disease became known in Spain as the ‘Naples Soldier’.

But though the Spanish flu didn’t start in Spain, that country did suffer quite badly with it. In the early 20th century, flu was viewed as a democratic disease – nobody was immune from it – but, even in the thick of the pandemic, it was noted that the disease struck unevenly. It ‘preferred’ certain age groups: the very young and the elderly, but also a middle cohort aged 20 to 40. It preferred men to women, with the exception of pregnant women, who were at particularly high risk.

These age- and gender-related patterns were repeated all over the world, but the virulence with which the flu struck also varied from place to place. Inhabitants of certain parts of Asia were a staggering 30 times more likely to die from the flu than those in parts of Europe. In general, Asia and Africa suffered the highest death rates, with the lowest seen in Europe, North America and Australia. But there was great variation within continents, too. African countries south of the Sahara experienced death rates two or even three times higher than those north of the desert, while Spain recorded one of the highest death rates in Europe – twice that in Britain, three times that in Denmark.

The unevenness didn’t stop there. In general, cities suffered worse than rural areas, but some cities suffered worse than others, and there was also variation within cities. Newly arrived immigrants tended to die more frequently than older, better-established groups, for example. In the countryside, meanwhile, one village might be decimated while another, apparently similar in every way, got away with a light dose.

What types of people caught the Spanish flu?

The flu seemed to strike with an element of randomness, and cruelly so. Because adults in the prime of life died in droves, unlucky communities imploded. Children were orphaned, elderly parents left to fend for themselves. People were at a loss to explain this apparent lottery, and it left them deeply disturbed. Attempting to describe the feeling it inspired in him, a French doctor in the city of Lyons wrote that it was quite unlike the “gut pangs” he had experienced while serving at the front. This was “a more diffuse anxiety, the sensation of some indefinable horror which had taken hold of the inhabitants of that town”.

It was only later, when epidemiologists zeroed in on the numbers, that patterns began to emerge, and the first elements of an explanation were put forward. Some of the variability could be explained by inequalities of wealth and caste – and, to the extent that it reflected these factors, skin colour. Bad diet, crowded living conditions and limited access to healthcare weakened the constitution, rendering the poor, immigrants and ethnic minorities more susceptible to infection. As French historian Patrick Zylberman put it: “The virus might well have behaved ‘democratically’, but the society it attacked was hardly egalitarian.”

Any other underlying disease made a person more susceptible to the Spanish flu, whereas prior exposure to the flu itself modulated the severity of a case. Remote communities without much historical experience of the disease suffered badly, as did cities that were bypassed by the first wave of the pandemic, because they were not immunologically ‘primed’ to the second. For example, Rio de Janeiro – capital of Brazil at the time – received only one wave of flu, in October 1918, and experienced a death rate two or three times higher than that recorded in American cities to the north that had received both the spring and autumn waves. And Bristol Bay in Alaska was spared until early 1919, but when the virus finally gained a foothold it reduced the bay’s Eskimo population by 40%.

Public health campaigns made a difference, despite the fact that medics did not understand the cause of the disease. Since time immemorial, whenever contagion is a threat humans have practised ‘social distancing’ – understanding instinctively that steering clear of infected individuals increases the chance of staying healthy. In 1918, social distancing took the form of quarantine zones, isolation wards and prohibitions on mass gatherings; where they were properly enforced, these measures slowed the spread. Australia kept out the autumn wave entirely by implementing an effective quarantine at its ports.

Exceptions proved the rule. In 1918 Persia was a failed state after years of being used as a pawn in the ‘Great Game’ – the struggle between the British and the Russians for control of the vast area between the Arabian and Caspian Seas. Its government was weak and nearly bankrupt, and it lacked a coherent sanitary infrastructure, so when the flu erupted in the north-eastern holy city of Mashhad in August 1918, no social distancing measures were imposed.

Within a fortnight every home and place of business in Mashhad was infected, and two-thirds of the city’s population fell sick that autumn. With no restrictions on movement, the flu spread outwards with pilgrims, soldiers and merchants to the four corners of the country. By the time Persia was again free of flu, it had lost between 8% and 22% of its population (that uncertainty reflecting the fact that, in a country in crisis, gathering statistics was hardly a priority). By way of comparison, even 8% equates to 20 times the flu-related mortality rate in Ireland.

Where disparities in rates of illness and death were perceived, people’s explanations reflected contemporary understanding – or, rather, misunderstanding – of infectious disease. When Charles Darwin laid out his theory of evolution by natural selection in On the Origin of Species (1859), he had not intended his ideas to be applied to human societies, but others of his time did just that, creating the ‘science’ of eugenics. Eugenicists believed that humanity comprised different ‘races’ that competed for survival, and by 1918 their thinking was mainstream in industrialised societies. Some eugenicists noted that poorer sectors of society were suffering disproportionately from the flu, which they attributed to a constitutional inferiority. They had also incorporated germ theory into their world view: if the poor and the working classes were more prone to infection, reasoned the eugenicists, they only had themselves to blame, because Pasteur had taught that infection was preventable.

Indian tensions

The terrible consequences of this line of thinking are illustrated nowhere better than in India. That land’s British colonisers had long taken the view that India was inherently unhygienic, and so had invested little in indigenous healthcare. As many as 18 million Indians died in the pandemic – the greatest loss in absolute numbers of any country in the world. But there would be a backlash. The underpowered British response to the spread of flu fuelled resentment within the independence movement. Tensions came to a head with the passing into law in early 1919 of the Rowlatt Act, which extended martial law in the country. This triggered peaceful protests, and on 13 April British troops fired into an unarmed crowd in Amritsar, killing hundreds of Indian people – a massacre that galvanised the independence movement.

The Spanish flu prompted uprisings elsewhere. The autumn of 1918 saw a wave of workers’ strikes and anti-imperialist protests across the world. Disgruntlement had been smouldering since before the Russian revolutions of 1917, but the flu fanned the flames by exacerbating what was already a dire supply situation, and by highlighting inequality. Even well-ordered Switzerland narrowly avoided a civil war in November 1918 after leftwing groups blamed the high number of flu deaths in the army on the government and military command.

There were still parts of the world where people had never heard of either Darwin or germ theory, and where the population turned to more tried-and-tested explanations. In the rural interior of China, for example, many people still believed that illness was sent by demons and dragons; they paraded figures of dragon kings through the streets in the hope of appeasing the irate spirits. A missionary doctor described going from house to house in Shanxi province in early 1919, and finding scissors placed in doorways – apparently to ward off demons “or perchance to cut them in two”.

Even in the modernised west, people vacillated. Death often seemed to strike without rhyme or reason. Many still remembered a more mystical, pre-Darwinian era, and four years of war had worn down psychological defences. Seeing how ill-equipped their men of science were to help them, many people came to believe that the pandemic was an act of god – divine retribution for their sins. In Zamora – the same Spanish city whose newspaper stated with such confidence that the agent of disease was Pfeiffer’s bacillus – the bishop defied the health authorities’ ban on mass gatherings and ordered people into the churches to placate “God’s legitimate anger”. This city subsequently recorded one of the highest death tolls from flu in Spain – a fact of which its inhabitants were aware, though they don’t seem to have held it against their bishop. Instead they awarded him a medal in recognition of his heroic efforts to end their suffering.

This exemplifies how responses to the flu reflected gulfs in understanding. The 1918 pandemic struck a world that was entirely unprepared for it, dealing a body blow to scientific hubris, and destabilising social and political orders for decades to come.

Laura Spinney is a journalist and the author of Pale Rider: The Spanish Flu of 1918 and How it Changed the World, (Jonathan Cape, June 2017).


This article first appeared in BBC World Histories, issue 4