This was hardly the first influenza pandemic, nor was it the only lethal one. But what made it so deadly? The answer lies in a perfect storm of global conflict, misinformation, and an invisible enemy we were only just beginning to understand.

How It All Began

The pandemic began mildly, with what seemed like an ordinary spring flu. Historians still debate where the 1918 influenza strain first emerged, but the earliest known cases appeared at a U.S. Army training camp in Kansas in March 1918. Within weeks, the illness had spread rapidly among soldiers and civilians alike.

The conditions of World War I (overcrowded military camps, global troop movements, and weakened immune systems) helped the virus travel faster than ever before. At the same time, government censorship and misinformation made matters worse. Determined to maintain public morale during wartime, many authorities downplayed the outbreak instead of preparing for it. The combination of rigid control and disregard for truth had dangerous consequences, which would soon become apparent.

The "Spanish" Flu

During World War I, many governments strictly controlled what the public could read in the news to protect morale. Reports of a new influenza spreading among troops were censored in countries like France, Britain, and the United States. Spain, however, remained neutral during the war, and its uncensored press freely reported on the outbreak. As a result, people abroad assumed the epidemic had started there, and the misleading name “Spanish flu” stuck. Ironically, Spain was one of the few countries telling the truth.

The Calm Before the Storm

By the summer of 1918, reported flu cases had dropped sharply. Many hoped that the outbreak had run its course, and that the worst was over. In hindsight, it was only the calm before the storm.

The first, mild wave of infections in spring had been so gentle that some physicians even questioned whether it was influenza at all. In July 1918, The Lancet published an article arguing that the illness seemed “of very short duration and so far absent of relapses or complications”. Few could have imagined that a far deadlier version of the same virus was already on its way.

The Second Wave

Within a few weeks of that Lancet article’s publication, a second pandemic wave swept around the world. Somewhere in Europe, a mutated strain of the Spanish flu virus had emerged that had the power to kill a perfectly healthy young man or woman within 24 hours of showing the first signs of infection.

In late August 1918, ships carrying troops left the English port city of Plymouth, unknowingly carrying infected soldiers. As these ships arrived in cities like Brest in France, Boston in the United States, and Freetown in West Africa, the second wave of the pandemic erupted. 

“The rapid movement of soldiers around the globe was a major spreader of the disease,” explains James Harris, a historian at Ohio State University who studies both infectious disease and World War I. “The entire military-industrial complex of moving lots of men and material in crowded conditions was certainly a huge contributing factor in the ways the pandemic spread.”

At first, the virus was so deadly that even medical investigators doubted it was influenza at all. Yet as later waves followed - one in early 1919 and another in 1920 - patterns emerged. Those who had survived the mild spring outbreak seemed largely protected from later infections, offering compelling evidence that all three waves were caused by the same virus.

Young Adults at Risk

Unlike most influenza outbreaks, which tend to strike the very young and the elderly, the 1918 virus targeted healthy adults in their twenties and thirties. In South African cities, people aged 20 to 40 accounted for around 60 percent of all deaths. In Chicago, mortality among that same age group was nearly five times higher than among those aged 40 to 60. A Swiss physician at the time observed that he “saw no severe cases in anyone over 50”.

Not only was it shocking that healthy young men and women were dying by the millions worldwide, but how quickly the disease took hold. Victims often coughed violently, hemorrhaging from their noses and mouths, and many drowned as their lungs filled with fluid.

One U.S. Army doctor described patients who rapidly progressed from flu-like symptoms to “the most vicious type of pneumonia”, their skin turning blue as they gasped for air. “It is only a matter of a few hours then until death comes”, he wrote.

Pathologists performing autopsies later found that the lungs of influenza victims resembled those of soldiers exposed to poison gas – a grim reminder of the war that raged alongside the pandemic.

Unprepared and Overwhelmed

The world of 1918 was woefully unprepared for a pandemic of this scale. Scientists had only recently discovered viruses, and most doctors still believed influenza was caused by bacteria. Without modern antibiotics, secondary infections like bacterial pneumonia often proved fatal (Penicillin, which would later save millions of lives, wasn’t discovered until 1928.).

In the absence of effective treatments, physicians tried nearly everything – from oxygen therapy to experimental vaccines targeting the wrong pathogens, and even outdated practices like bloodletting. Nothing worked.

The sheer number of deaths quickly overwhelmed healthcare systems. Makeshift morgues filled up, and special trains were used to transport the dead.

^{A hospital in Kansas during the Spanish flu epidemic in 1918. / Wikimedia Commons}

Public health efforts were inconsistent and often undermined by a shortage of medical staff. Many nurses were deployed to military camps, leaving civilian hospitals desperately understaffed. In the United States, racial segregation compounded the crisis: African American nurses were barred from service until late in the pandemic, further depleting an already strained healthcare workforce.

Downplaying the Severity

In many places, public health officials downplayed the crisis to avoid panic and maintain wartime morale. Cities issued reassurances that proved dangerously misleading. In Chicago, the public health commissioner insisted there was “nothing to fear” and called it “only ordinary influenza.” In Philadelphia, newspapers repeated similar claims, even as hospitals overflowed and bodies filled temporary morgues.

This disconnect between official statements and visible suffering further eroded public trust.

The social consequences were stark. Communities that once cared for one another grew distant: neighbors refused to help the sick, and volunteers hesitated to enter infected homes. One relief organizer lamented that “hundreds of women who had the vanity to imagine themselves angels of mercy” turned away while children went hungry. In rural Kentucky, the Red Cross reported people “starving to death not from lack of food, but because the well were panic-stricken and would not go near the sick.”

Public Health Measures

Once it was understood that the flu was spread by respiratory droplets, authorities introduced various prevention measures. Public education campaigns urged people not to cough or sneeze openly and to avoid “careless disposal of nasal discharges.” Masks were encouraged, and ventilation was seen as vital; in San Francisco, for example, court sessions were held outdoors to reduce transmission.

1 Open-air police court being held in Portsmouth Square, San Francisco.

2 Newspaper article (The Washington Times, September 27, 1918) showing gauze mask recommended by the Red Cross to halt spread of the Spanish flu

3 Headlines from newspapers in Chicago, Illinois, U.S. at the time of the 1918 Spanish flu. 

4 Advertisement for the Chicago School of Nursing. Nurses were in short supply and high demand during the epidemic.

Across the United States, theaters, schools, and public gatherings were shut down. The American Public Health Association recommended staggering opening hours for shops and factories and urged people to walk to work instead of using public transport.

Even world leaders weren’t spared: during the 1919 Versailles Peace Conference, U.S. President Woodrow Wilson reportedly collapsed, and some historians suspect he was weakened by influenza. An eerie reminder that no one, not even the powerful, was immune.

A Mystery and Its Legacy

Despite its terrifying impact, much about the 1918 flu remained a mystery for decades, especially for why the virus struck hardest at those in the prime of life. Though the exact reason for why this was the case is still debated, many now believe this was due to a phenomenon called a cytokine storm, an overreaction of the body’s own immune system. In other words, the very strength of a young, healthy immune response became fatal.

The so-called "Spanish flu" left a lasting legacy on the world. It exposed the vulnerabilities of modern society to pandemics and the consequences of government misinformation and lack of preparedness. Over a century later, its lessons still echo, especially in light of recent global health crises. The 1918 pandemic today serves as a reminder of how quickly a virus can spread, and how essential truth and preparedness are in protecting us all.