The 1918–1920 influenza pandemic, commonly referred to as the Great Influenza Epidemic or the Spanish Flu, was an exceptionally deadly global outbreak caused by the H1N1 influenza A virus.

The first case was reported in Kansas, United States, in late spring 1918, where it was initially termed "epidemic influenza" or "the grip." Early reports from Spain appeared on May 21, describing it as a "three-day fever."

By April, cases had also been identified in France, Germany, and the United Kingdom.

The third wave, occurring in winter 1918-1919, was less lethal than the second wave but more severe than the first.

It further strained medical resources and contributed significantly to the overall death toll.

This wave saw the resurgence of the virus in a slightly less virulent form, but it still caused widespread illness and death, particularly in communities already weakened by the previous waves.

The pandemic's spread and impact were exacerbated by the First World War, which facilitated the virus's global transmission through troop movements and crowded military camps.

Soldiers traveling between continents and countries carried the virus with them, accelerating its spread.

The war also contributed to poor living conditions, malnutrition, and weakened immune systems, making populations more susceptible to the virus.

The widespread morbidity and mortality disrupted societies and economies, leaving lasting impacts on global health and medical practices.

The pandemic underscored the importance of public health measures, such as quarantine, social distancing, and the use of masks, and highlighted the need for international cooperation in managing global health crises.

The origins of the Spanish flu are shrouded in uncertainty, partly due to wartime censorship and misinformation.

During the First World War, belligerent countries suppressed unpleasant news to maintain morale, while neutral Spain freely reported on the pandemic.

This transparency gave the misleading impression that Spain was the epicenter of the outbreak, leading to the term "Spanish flu."

This situation is illustrated by a dispatch from The Times of London dated June 2, 1918, titled "The Spanish Epidemic," where a correspondent in Madrid reported 100,000 cases of "…the unexplained disease...clearly of a gripal character."

Three weeks later, The Times published an article that indirectly referenced "Spanish influenza," and advertisements for "Spanish influenza prevention" began to appear, such as the Formamint tablet ad.

In Russia, the pandemic was colloquially referred to as "Ispánka (the Spanish lady) is in town," further entrenching the erroneous belief that Spain was the origin.

This misconception persisted because Spain, being a neutral nation, had no need to maintain an appearance of readiness for battle.

Its newspapers freely reported on the epidemic's effects, including the illness of King Alfonso XIII.

The Spanish reports were so detailed and prominent that they overshadowed the outbreak's presence in other countries, which were equally affected but less forthcoming due to wartime propaganda efforts.

In reality, the outbreak did not start in Spain.

Historical evidence suggests the flu may have originated elsewhere, with theories pointing to locations such as Kansas in the United States, where the first recorded case on March 4, 1918, involved Albert Gitchell, an army cook at Camp Funston.

Additionally, earlier cases had been identified in January 1918 in Haskell County, Kansas, where local physician Loring Miner alerted the Public Health Reports journal to the unusual severity of the flu.

The pandemic's rapid spread was facilitated by the conditions of the First World War.

Military camps, troop movements, and congested living quarters provided ideal environments for the virus to propagate.

The flu quickly infiltrated Europe, spreading from military camps in the United States to battlefields and civilian populations across France, Great Britain, Italy, and Spain, and reaching Wroclaw and Odessa by May 1918.

Spanish flu presented a range of symptoms, from typical flu-like signs to severe and often fatal conditions.

Initial symptoms resembled those of seasonal influenza: high fever, chills, fatigue, headaches, and muscle aches.

However, many sufferers quickly developed more alarming symptoms, such as a deep, wracking cough, severe sore throat, and a pronounced sense of malaise.

The Spanish flu also led to secondary bacterial infections, such as bacterial pneumonia, which compounded the suffering and mortality rates.

These infections were difficult to treat effectively, given the limited medical knowledge and lack of antibiotics at the time.

Patients with these secondary infections often experienced high fevers, chest pain, and a productive cough with blood-tinged sputum.

Neurological symptoms were also reported, including delirium and, in some cases, encephalitis (brain inflammation), which could lead to long-term cognitive impairments.

The severe systemic inflammation caused by the flu strained the cardiovascular system, sometimes leading to heart failure.

The high mortality rate among young adults, rather than the very young or elderly, was a peculiar aspect of this pandemic.

This demographic often suffered from a hyperactive immune response, known as a cytokine storm, which led to severe lung damage and contributed significantly to the high death toll.

Overall, the Spanish flu's symptoms and medical effects were devastating, overwhelming healthcare systems and leaving lasting impacts on global health.

The origins of the Spanish flu pandemic remain a subject of debate among historians and epidemiologists due to conflicting theories and a lack of conclusive historical evidence.

Despite earlier cases, the pandemic is traditionally marked as beginning on March 4, 1918, with the documented case of Albert Gitchell, an army cook at Camp Funston in Kansas, United States.

However, the illness had already been identified in January 1918, about 200 miles away in Haskell County.

The flu quickly infiltrated Europe, spreading to France, Great Britain, Italy, and Spain, reaching Wroclaw and Odessa by May 1918.

The Treaty of Brest-Litovsk in March 1918 further contributed to the spread as Germany released Russian prisoners of war, who then carried the virus back to their home country.

The interconnectedness of the war efforts and the extensive movement of people played a crucial role in the pandemic's global reach.

The mild nature of the first wave is further evidenced by the lack of major public health responses.

There were no reported quarantines during the first three months of 1918, reflecting a general underestimation of the potential severity of the outbreak.

However, the flu's impact on military operations during World War I was significant. The illness incapacitated almost 900,000 German soldiers, and approximately 75% of the British and French forces were affected, severely hampering military efforts.

The second wave of the Spanish flu pandemic began in the latter half of August 1918. This wave was notably more deadly and widespread than the first, primarily due to its likely introduction by ships from Brest, France.

Brest was a significant port for American troops and French recruits involved in World War I, and the virus possibly arrived there with these soldiers. From Brest, it spread to Boston and Freetown, Sierra Leone.

At Camp Devens, approximately 30 miles west of Boston, and the Boston Navy Yard, U.S. military installations were quickly affected.

These locations served as crucial points for troops being deployed to Europe, facilitating the flu's rapid dissemination across North America within two months.

Military movements further propelled the virus into Central and South America. Ships carried the flu to Brazil and the Caribbean, with significant outbreaks noted.

In Europe, the second wave originated and spread southwest to northeast, affecting Russia and reaching Iran. It spread through the holy city of Mashhad and moved across Asia, exacerbated by the Russian Civil War and the extensive reach of the Trans-Siberian Railway.

By September 1918, the flu had reached India, with China and Japan reporting cases by October. In conjunction with the Armistice celebrations on November 11, 1918, Lima and Nairobi experienced significant outbreaks.

By December, the intensity of the second wave had diminished.

The second wave proved far deadlier than the first. While the initial wave primarily affected the elderly and those with preexisting health conditions, the second wave caused severe illness and high mortality rates among younger, healthier individuals.

This shift was likely due to a mutation in the virus, which led to more severe respiratory complications. October 1918 marked the peak of the pandemic's fatality rate.

Between September and December 1918, the United States reported 292,000 deaths, a significant increase compared to the 26,000 deaths during the same period in 1915.

The Netherlands recorded over 40,000 deaths from influenza and acute respiratory illnesses, and Bombay, with a population of 1.1 million, saw 15,000 deaths. In India alone, the flu epidemic claimed an estimated 12.5–20 million lives in the last quarter of 1918.

The third wave of the Spanish flu pandemic occurred during the winter of 1918-1919 and extended into the spring of 1919.

This phase, while less deadly than the second wave, was still significantly more lethal than the initial outbreak.

The third wave is characterized by its recurrence in populations already weakened by the earlier waves, compounded by the harsh winter conditions, which exacerbated the spread and impact of the virus.

The third wave began to manifest in January 1919. Many cities that had experienced devastation during the second wave saw a resurgence of cases.

The virus continued to spread along well-established routes of human movement and interaction, heavily influenced by the aftermath of the First World War.

Troop demobilizations, the return of soldiers to their home countries, and the movement of laborers and refugees played critical roles in this renewed spread.

The third wave had a profound impact on public health systems and societal norms. Hospitals, already stretched thin from the previous waves, struggled to cope with the influx of patients.

Medical staff, many of whom had been infected during earlier waves, were overworked and exhausted, leading to severe shortages in healthcare provision.

Public health measures varied in effectiveness and enforcement.

The impact on Aboriginal Australians was particularly severe. Many Aboriginal communities lacked access to adequate healthcare and were already suffering from poor living conditions, malnutrition, and other diseases. Certain Aboriginal communities saw a mortality rate of 50%.

The Spanish flu exacerbated these issues, leading to high mortality rates. The lack of immunity and limited medical resources in these communities meant that the flu spread quickly and lethally, with entire communities being decimated.

Throughout the spring and summer, there were a spate of isolated or solitary instances of flu being reported across the United States.

Even though there had been an increase in isolated cases since September, Chicago began to see one of the first significant flu outbreaks in the middle of January.

Days after Chicago's rapid increase in cases, it was clear that the flu was spreading there even more quickly than it had in winter 1919, though there were fewer fatalities.

The number of new cases in the city surpassed the peak of the 1919 wave within a week. New York City started to experience a dramatic rise of cases around the same time, and other cities throughout the nation quickly followed.

Other US cities were particularly heavily struck, with death rates exceeding those of the entire year 1918. These cities included Detroit, Milwaukee, Kansas City, Minneapolis, and St. Louis.

Early in 1920, when the pandemic reached its height in the Territory of Hawaii, 1,489 people there died from flu-related causes, compared to 615 in 1918 and 796 in 1919.

Similarly, Nenana, Alaska, missed the worst of the epidemic for the first two years, but by May 1920, the town had been overrun by an outbreak.

According to reports, the majority of the town's residents contracted the disease within the first two weeks of the month; 10% of the population is thought to have perished.

Western Europe, in contrast, experienced a "benign" outbreak, with the age distribution of fatalities beginning to resemble that of a seasonal flu.

Between January and April 1920, five European nations—Spain, Denmark, Finland, Germany, and Switzerland—recorded a late high.

Early 1920 saw a late wave in Peru, and late 1919 to early 1920 saw one in Japan, with the last cases occurring in March.

The Spanish flu pandemic featured unusually high mortality rates among young adults, a deviation from the typical pattern of influenza epidemics, which generally affect the very young and the elderly more severely. Scientists have proposed several explanations for this anomaly.

One theory suggests that a six-year climate anomaly prior to the pandemic influenced disease vector migration, potentially increasing the spread of pathogens through water bodies.

During the pandemic, the absence of antiviral drugs and antibiotics posed severe challenges for medical practitioners. Doctors resorted to a diverse array of treatments with varying degrees of effectiveness.

Commonly used medications included aspirin, quinine, arsenics, digitalis, strychnine, Epsom salts, castor oil, and iodine.

Aspirin, for example, was widely recommended, sometimes in dangerously high doses, leading to aspirin toxicity in many patients.

The desperation of the time led to the proliferation of numerous failed or fake treatments.

Some of these were based on superstition or incorrect medical theories.

For instance, the use of camphor and mercury in various forms was common, despite their lack of effectiveness and potential harm.

Patent medicines, often containing alcohol, opium, or other narcotics, were marketed aggressively as cures, exploiting the fear and uncertainty of the public.

Quack remedies flourished as well. Snake oil salesmen peddled concoctions that promised miraculous recoveries but delivered little more than false hope.

The lack of regulation and the urgent demand for cures created a fertile ground for these fraudulent treatments.

Despite the prevalence of ineffective and dangerous treatments, the Spanish flu pandemic did spur some significant medical advancements.

The experience highlighted the need for better understanding and treatment of viral infections and secondary bacterial infections.

This period underscored the importance of scientific research and evidence-based medicine.

The Spanish flu pandemic of 1918-1920, concurrent with the closing stages of the FirstWorld War, significantly impacted both the warring sides and the post-war recovery efforts.

The overlap of a devastating pandemic with a global conflict exacerbated the challenges faced by military and civilian populations, influencing the outcomes of military engagements and the subsequent peace process.

The spread of the Spanish flu among soldiers had a direct impact on the capacity of military forces.

An increase in soldiers unable to fight due to flu infection reduced the number of active combatants, weakening military operations.

Reports from military camps in Europe and the United States documented high rates of infection, with some units experiencing up to a 40% reduction in fighting capability.

This loss of manpower was critical during the final offensives of the war, affecting the strategic planning and execution of military operations.

This exacerbated the overall morbidity and mortality, contributing to the staggering death toll of the pandemic.

The influx of flu patients placed an enormous strain on medical units, which were already overwhelmed by battlefield injuries.

Military hospitals and medical staff were stretched to their limits, trying to manage both combat casualties and flu victims.

The lack of effective treatments for the flu compounded the problem, as medical personnel struggled to provide adequate care with limited resources.

The unsanitary conditions in military camps and civilian areas further facilitated the spread of the flu.

In the trenches, soldiers lived in close proximity to each other, often in damp and muddy environments with little access to clean water and proper sanitation.

These conditions were ideal for the transmission of the virus, leading to widespread outbreaks that decimated entire units.

Similarly, civilian populations living in overcrowded and unsanitary urban areas experienced high infection rates, contributing to the overall death toll.

The movement of refugees during and after the war played a significant role in spreading the flu. Displaced by the conflict, refugees moved from area to area seeking shelter, often carrying the virus with them.

This constant movement facilitated the transmission of the flu across borders and into new populations, making containment efforts exceedingly difficult.

The lack of coordinated international response to the refugee crisis further exacerbated the spread of the disease.

The germ theory of disease was still relatively new, and many public health officials did not fully understand how to combat the virus.

Quarantine measures, where implemented, were often too late or poorly enforced.

The use of masks and social distancing was not widespread, and public gatherings continued in many areas, facilitating the spread of the virus.

This lack of effective public health strategies allowed the flu to spread unchecked through both military and civilian populations.

The Spanish Flu pandemic of 1918-1919 had profound and immediate effects on national and global economies.

As the deadly influenza outbreak claimed an estimated 50 million lives worldwide, it severely disrupted economic activities and exacerbated the social and economic turmoil already caused by the First World War.

In the immediate aftermath, significant labour shortages arose due to high mortality rates, which drastically impacted industrial and agricultural production.

The Spanish Flu also exposed the inadequacies of public health systems and the lack of international cooperation in addressing global health crises.

The failure to effectively manage the pandemic fostered public distrust in governments and institutions, contributing to political instability.

In the long term, the compounded crises from the pandemic and post-war challenges set the stage for the Great Depression in the 1930s, further destabilizing economies and societies. The resultant economic hardships and political instability were crucial factors in the rise of fascist regimes in Europe.

The inability of weakened democracies to effectively address these issues ultimately led to the aggressive expansionism and conflicts that sparked the Second World War.

Thus, while not a direct cause, the Spanish Flu pandemic played a significant role in shaping the volatile global environment that contributed to the outbreak of the war.

Eventually, the Spanish Flu began to fade from the public consciousness, overshadowed by the First World War and its aftermath.

As terrible as the flu was, its horror was overshadowed by the four years of death and destruction which dominated the media and remained firmly in the public eye.

When people read the obituaries, they saw the influenza deaths next to the war or postwar dead. The virus may not have had a significant psychological effect or may have appeared to be a continuation of the war's horrors, especially in Europe where the war's toll was great.

The pandemic had profound and far-reaching effects on the global stage, particularly in the 1920s and 1930s, indirectly contributing to the conditions that led to the outbreak of the Second World War.

This deadly influenza outbreak killed an estimated 50 million people worldwide, exacerbating the already severe social and economic disruptions caused by the First World War.

The Spanish Flu pandemic also highlighted the inadequacies of public health systems and the lack of international cooperation in addressing global health crises.

This failure to effectively manage the pandemic fostered public distrust in governments and institutions, contributing to political instability.

As societies grappled with these challenges, extremist political movements found fertile ground for growth.

In Germany, for instance, the economic and social turmoil created a breeding ground for radical ideologies, including the rise of the Nazi Party.

The Pandemic had a profound impact on world politics, significantly influencing both immediate and long-term geopolitical landscapes.

The pandemic struck during the final stages of the First World War, severely affecting soldiers and civilians alike, which complicated military operations and hastened the war's end.

Additionally, the pandemic exacerbated economic instability and social unrest, contributing to political upheavals.

For instance, in Russia, the flu, combined with famine, devastated urban populations, pushing Lenin to implement one of the first modern public healthcare systems to stabilize the country​​.

Similarly, the pandemic's aftermath influenced the 1920 U.S. presidential election, with Warren G. Harding's call for a "return to normalcy" resonating with a population exhausted by war and disease​​.

As the world moved into the 1930s, these compounded crises set the stage for the Great Depression, further destabilizing economies and societies.

The resultant economic hardships and political instability were crucial factors in the rise of fascist regimes in Europe.

The inability of weakened democracies to effectively address these issues ultimately led to the aggressive expansionism and conflicts that sparked the Second World War.

Thus, the Spanish Flu pandemic, while not a direct cause, played a significant role in shaping the volatile global environment that led to the war.