History

Timeline

First wave of early 1918

The pandemic is conventionally marked as having begun on 4 March 1918 with the recording of the case of Albert Gitchell, an army cook at Camp Funston in Kansas, United States, despite there likely having been cases before him. The disease had been observed in Haskell County in January 1918, prompting local doctor Loring Miner to warn the US Public Health Service's academic journal. Within days, 522 men at the camp had reported sick. By 11 March 1918, the virus had reached Queens, New York. Failure to take preventive measures in March/April was later criticized.

As the US had entered World War I, the disease quickly spread from Camp Funston, a major training ground for troops of the American Expeditionary Forces, to other US Army camps and Europe, becoming an epidemic in the Midwest, East Coast, and French ports by April 1918, and reaching the Western Front by the middle of the month. It then quickly spread to the rest of France, Great Britain, Italy, and Spain and in May reached Breslau and Odessa. After the signing of the Treaty of Brest-Litovsk (March 1918), Germany started releasing Russian prisoners of war, who then brought the disease to their country. It reached North Africa, India, and Japan in May, and soon after had likely gone around the world as there had been recorded cases in Southeast Asia in April. In June an outbreak was reported in China. After reaching Australia in July, the wave started to recede.

The first wave of the flu lasted from the first quarter of 1918 and was relatively mild. Mortality rates were not appreciably above normal; in the United States ~75,000 flu-related deaths were reported in the first six months of 1918, compared to ~63,000 deaths during the same time period in 1915. In Madrid, Spain, fewer than 1,000 people died from influenza between May and June 1918. There were no reported quarantines during the first quarter of 1918. However, the first wave caused a significant disruption in the military operations of World War I, with three-quarters of French troops, half the British forces, and over 900,000 German soldiers sick.

Deadly second wave of late 1918

The second wave began in the second half of August, probably spreading to Boston and Freetown, Sierra Leone, by ships from Brest, where it had likely arrived with American troops or French recruits for naval training. From the Boston Navy Yard and Camp Devens (later renamed Fort Devens), about 30 miles west of Boston, other U.S. military sites were soon afflicted, as were troops being transported to Europe. Helped by troop movements, it spread over the next two months to all of North America, and then to Central and South America, also reaching Brazil and the Caribbean on ships. In July 1918, the Ottoman Empire saw its first cases in some soldiers. From Freetown, the pandemic continued to spread through West Africa along the coast, rivers, and the colonial railways, and from railheads to more remote communities, while South Africa received it in September on ships bringing back members of the South African Native Labour Corps returning from France. From there it spread around southern Africa and beyond the Zambezi, reaching Ethiopia in November. On September 15, New York City saw its first fatality from influenza. The Philadelphia Liberty Loans Parade, held in Philadelphia, Pennsylvania, on 28 September 1918 to promote government bonds for World War I, resulted in 12,000 deaths after a major outbreak of the illness spread among people who had attended the parade.

From Europe, the second wave swept through Russia in a southwest–northeast diagonal front, as well as being brought to Arkhangelsk by the North Russia intervention, and then spread throughout Asia following the Russian Civil War and the Trans-Siberian railway, reaching Iran (where it spread through the holy city of Mashhad), and then later India in September, as well as China and Japan in October. The celebrations of the Armistice of 11 November 1918 also caused outbreaks in Lima and Nairobi, but by December the wave was mostly over.

The second wave of the 1918 pandemic was much more deadly than the first. The first wave had resembled typical flu epidemics; those most at risk were the sick and elderly, while younger, healthier people recovered easily. October 1918 was the month with the highest fatality rate of the whole pandemic. In the United States, ~292,000 deaths were reported between September–December 1918, compared to ~26,000 during the same time period in 1915. The Netherlands reported 40,000+ deaths from influenza and acute respiratory disease, Bombay reported ~15,000 deaths in a population of 1.1 million. The 1918 flu pandemic in India was especially deadly, with an estimated 12.5–20 million deaths in the last quarter of 1918 alone.page needed

Third wave of 1919

In January 1919, a third wave of the Spanish Flu hit Australia, where it killed 12,000 following the lifting of a maritime quarantine, and then spread quickly through Europe and the United States, where it lingered through the Spring and until June 1919. It primarily affected Spain, Serbia, Mexico and Great Britain, resulting in hundreds of thousands of deaths. It was less severe than the second wave but still much more deadly than the initial first wave. In the United States, isolated outbreaks occurred in some cities including Los Angeles, New York City, Memphis, Nashville, San Francisco and St. Louis. Overall American mortality rates were in the tens of thousands during the first six months of 1919.

Fourth wave of 1920

In spring 1920, a fourth wave occurred in isolated areas including New York City, Switzerland, Scandinavia, and some South American islands. New York City alone reported 6,374 deaths between December 1919 and April 1920, almost twice the number of the first wave in spring 1918. Other U.S. cities including Detroit, Milwaukee, Kansas City, Minneapolis and St. Louis were hit particularly hard, with death rates higher than all of 1918. Peru experienced a late wave in early 1920, and Japan had one from late 1919 to 1920, with the last cases in March. In Europe, five countries (Spain, Denmark, Finland, Germany and Switzerland) recorded a late peak between January–April 1920.

Potential origins

Despite its name, historical and epidemiological data cannot identify the geographic origin of the Spanish flu. However, several theories have been proposed.

United States

The first confirmed cases originated in the United States. Historian Alfred W. Crosby stated in 2003 that the flu originated in Kansas, and popular author John M. Barry described a January 1918 outbreak in Haskell County, Kansas, as the point of origin in his 2004 article.

A 2018 study of tissue slides and medical reports led by evolutionary biology professor Michael Worobey found evidence against the disease originating from Kansas, as those cases were milder and had fewer deaths compared to the infections in New York City in the same period. The study did find evidence through phylogenetic analyses that the virus likely had a North American origin, though it was not conclusive. In addition, the haemagglutinin glycoproteins of the virus suggest that it originated long before 1918, and other studies suggest that the reassortment of the H1N1 virus likely occurred in or around 1915.

Europe

The major UK troop staging and hospital camp in Étaples in France has been theorized by virologist John Oxford as being at the center of the Spanish flu. His study found that in late 1916 the Étaples camp was hit by the onset of a new disease with high mortality that caused symptoms similar to the flu. According to Oxford, a similar outbreak occurred in March 1917 at army barracks in Aldershot, and military pathologists later recognized these early outbreaks as the same disease as the Spanish flu. The overcrowded camp and hospital was an ideal environment for the spread of a respiratory virus. The hospital treated thousands of victims of poison gas attacks, and other casualties of war, and 100,000 soldiers passed through the camp every day. It also was home to a piggery, and poultry was regularly brought in from surrounding villages to feed the camp. Oxford and his team postulated that a precursor virus, harbored in birds, mutated and then migrated to pigs kept near the front.

A report published in 2016 in the Journal of the Chinese Medical Association found evidence that the 1918 virus had been circulating in the European armies for months and possibly years before the 1918 pandemic. Political scientist Andrew Price-Smith published data from the Austrian archives suggesting the influenza began in Austria in early 1917.

A 2009 study in Influenza and Other Respiratory Viruses found that Spanish flu mortality simultaneously peaked within the two-month period of October and November 1918 in all fourteen European countries analyzed, which is inconsistent with the pattern that researchers would expect if the virus had originated somewhere in Europe and then spread outwards.

China

In 1993, Claude Hannoun, the leading expert on the Spanish flu at the Pasteur Institute, asserted the precursor virus was likely to have come from China and then mutated in the United States near Boston and from there spread to Brest, France, Europe's battlefields, the rest of Europe, and the rest of the world, with Allied soldiers and sailors as the main disseminators. Hannoun considered several alternative hypotheses of origin, such as Spain, Kansas, and Brest, as being possible, but not likely. In 2014, historian Mark Humphries argued that the mobilization of 96,000 Chinese laborers to work behind the British and French lines might have been the source of the pandemic. Humphries, of the Memorial University of Newfoundland in St. John's, based his conclusions on newly unearthed records. He found archival evidence that a respiratory illness that struck northern China (where the laborers came from) in November 1917 was identified a year later by Chinese health officials as identical to the Spanish flu. However, no tissue samples have survived for modern comparison. Nevertheless, there were some reports of respiratory illness on parts of the path the laborers took to get to Europe, which also passed through North America.

One of the few regions of the world seemingly less affected by the Spanish flu pandemic was China, where several studies have documented a comparatively mild flu season in 1918. (Although this is disputed due to lack of data during the Warlord Period, see Around the globe.) This has led to speculation that the Spanish flu pandemic originated in China, as the lower rates of flu mortality may be explained by the Chinese population's previously acquired immunity to the flu virus.

A report published in 2016 in the Journal of the Chinese Medical Association found no evidence that the 1918 virus was imported to Europe via Chinese and Southeast Asian soldiers and workers and instead found evidence of its circulation in Europe before the pandemic. The 2016 study suggested that the low flu mortality rate (an estimated one in a thousand) found among the Chinese and Southeast Asian workers in Europe meant that the deadly 1918 influenza pandemic could not have originated from those workers. Further evidence against the disease being spread by Chinese workers was that workers entered Europe through other routes that did not result in a detectable spread, making them unlikely to have been the original hosts.