Spanish Flu Pandemic Timeline

The first known cases of the influenza that would become the Spanish flu were reported among soldiers at Camp Funston in Fort Riley, Kansas. Within weeks, hundreds of soldiers fell ill, and the virus spread with troops as the United States mobilized for World War I.

Just a week after the initial outbreak at Camp Funston, cases of the mysterious influenza appeared in Queens, New York, demonstrating how quickly the virus was moving through military installations and densely populated urban areas.

As American Expeditionary Forces crossed the Atlantic to join the fighting in France, they carried the influenza virus with them. Crowded transport ships and trenches became ideal environments for transmission, seeding outbreaks across Western Europe.

By late April 1918, the influenza had reached Brest, France, and soon spread to British and French troops on the Western Front and into civilian populations. The illness became known as the 'three-day fever' for its typically brief but debilitating course.

Spain, a neutral country during World War I, did not censor its press, so newspapers there freely reported the epidemic's toll, including the illness of King Alfonso XIII. This gave the false impression that Spain was especially hard hit, and the pandemic became known as the 'Spanish flu.'

The first wave of the pandemic, while highly contagious, was relatively mild, with most victims recovering within days. By midsummer 1918, case numbers declined significantly, leading many public health officials to believe the outbreak had passed.

The second wave of the Spanish flu proved far more lethal than the first, killing healthy young adults in addition to the very young and old. It ravaged war-torn Europe, overwhelming hospitals already strained by World War I casualties.

A far deadlier mutation of the virus appeared at Camp Devens near Boston in September 1918. Victims developed severe pneumonia, with some dying within hours of showing symptoms. The camp's physician described victims turning blue as their lungs filled with fluid.

Despite warnings from physicians, Philadelphia held a massive Liberty Loan parade attended by some 200,000 people. Within days, thousands of Philadelphians fell ill, and the city suffered one of the highest death rates of any American city, with over 12,000 deaths.

October 1918 was the deadliest month of the pandemic in the United States, with approximately 195,000 Americans dying from influenza and its complications. Cities closed schools, theaters, churches, and businesses; some banned public gatherings entirely.

A third wave of the pandemic swept through many parts of the world in early 1919. Though less deadly than the second wave, it still caused significant mortality before finally subsiding in the spring, marking the beginning of the end of the pandemic's acute phase.

While negotiating the Treaty of Versailles, President Woodrow Wilson contracted a severe case of influenza. Some historians believe the illness weakened him physically and mentally during critical negotiations, possibly influencing concessions he made to European allies.

A final wave of the pandemic struck in early 1920, hitting areas such as New York City, Scandinavia, and some isolated regions that had largely escaped earlier waves. Mortality was lower than in previous waves, and the pandemic faded afterward.

In the years following the pandemic, countries like Norway analyzed their response data and found that coordinated interventions such as school closures and bans on public gatherings reduced peak mortality, informing future public health planning.

By mid-1920, the Spanish flu pandemic had largely subsided. Why it ended remains unclear; one theory suggests the virus mutated toward less lethal forms, while another holds that so many people had been infected that herd immunity limited further spread.

In 1930, scientists isolated swine influenza virus from pigs in the United States, finding it closely related to the 1918 pandemic strain. This discovery supported theories linking the Spanish flu to an H1N1 influenza A virus.

Image source: Influenza A virus subtype H1N1

British scientists at the National Institute for Medical Research first isolated human influenza virus in 1933, fifteen years after the pandemic. This breakthrough enabled the development of vaccines and deeper understanding of influenza viruses.

Image source: Influenza