1918 flu pandemic The 1918 flu pandemic ( the Spanish Flu ) was an influenza pandemic , and the first of the two pandemics involving H1N1 influenza virus ( the follow - up was the 2009 flu pandemic ) . It was an unusually severe and deadly pandemic that spread across the world . Historical and epidemiological data are inadequate to identify the geographic origin . Most victims were healthy young adults , in contrast to most influenza outbreaks which predominantly affect juvenile , elderly , or weakened patients . The flu pandemic was implicated in the outbreak of encephalitis lethargica in the 1920s . The pandemic lasted from June 1918 to December 1920 , spreading even to the Arctic and remote Pacific islands . Between 50 and 100 million died , making it one of the deadliest natural disasters in human history . Even using the lower estimate of 50 million people , 3 % of the world ' s population ( 1 . 8 billion at the time ) died of the disease . Some 550 million , or 32 % ( ≈1 / 3 ) , were infected . Tissue samples from frozen victims were used to reproduce the virus for study . This research concluded , among other things , that the virus kills through a cytokine storm ( overreaction of the body ' s immune system ) , which perhaps explains its unusually severe nature and the concentrated age profile of its victims . The strong immune system reactions of young adults ravaged the body , whereas those of the weaker immune systems of children and middle - aged adults resulted in fewer deaths . Origins of name . Although the first cases were registered in the continental U . S . and the rest of Europe long before getting to Spain , the 1918 pandemic received its nickname " Spanish flu " because Spain , a neutral country in WWI , had no censorship of news regarding the disease and its consequences . Spanish King Alfonso XIII became gravely ill and was the highest - profile patient about whom there was coverage . Hence the widest and most reliable news coverage came from Spain , giving the false impression that Spain was most affected . History . World War I did not cause the flu , but the close troop quarters and massive troop movements hastened the pandemic and probably both increased transmission and augmented mutation ; it may also have increased the lethality of the virus . Some speculate that the soldiers ' immune systems were weakened by malnourishment as well as the stresses of combat and chemical attacks , increasing their susceptibility . Andrew Price - Smith has made the controversial argument that the virus helped tip the balance of power in the latter days of the war towards the Allied cause . He provides data that the viral waves hit the Central Powers before they hit the Allied powers , and that both morbidity and mortality in Germany and Austria were considerably higher than in Britain and France . A large factor in the worldwide occurrence of this flu was increased travel . Modern transportation systems made it easier for soldiers , sailors , and civilian travelers to spread the disease . In the United States the disease was first observed at Haskell County , Kansas in January 1918 . On 4 March 1918 , company cook Albert Gitchell reported sick at Fort Riley , Kansas . Within days , 522 men at the camp had reported sick . By March 11 , 1918 the virus had reached Queens , New York . In August 1918 , a more virulent strain appeared simultaneously in Brest , France , in Freetown , Sierra Leone , and in the U . S . at Boston , Massachusetts . The Allies of World War I came to call it the Spanish flu , primarily because the pandemic received greater press attention after it moved from France to Spain in November 1918 . Spain was not involved in the war and had not imposed wartime censorship . Theories about source . Some theorized that the flu originated in the Far East . Dr . C . Hannoun , leading expert of the 1918 flu for the Institut Pasteur , asserted that the former virus was likely to have come from China , mutated in the United States near Boston , and spread to Brest , France , Europe ' s battlefields , Europe , and the world using Allied soldiers and sailors as main spreaders . Hannoun considered several other theories of origin , such as Spain , Kansas , and Brest , as being possible but not likely . Historian Alfred W . Crosby speculated that the flu originated in Kansas . Political scientist Andrew Price - Smith published data from the Austrian archives suggesting that the influenza had earlier origins , beginning in Austria in the spring of 1917 . Popular writer John Barry echoed Crosby in describing Haskell County , Kansas as the likely point of origin . Investigative work by a British team , led by virologist John Oxford of St Bartholomew ' s Hospital and the Royal London Hospital , has suggested that a major British troop staging camp in Étaples , France was at the center of the 1918 flu pandemic or was the location of a significant precursor virus . Mortality . The global mortality rate from the 1918 / 1919 pandemic is not known , but it is estimated that 10 % to 20 % of those who were infected died . With about a third of the world population infected , this case - fatality ratio means that 3 % to 6 % of the entire global population died . Influenza may have killed as many as 25 million in its first 25 weeks . Older estimates say it killed 40 – 50 million people while current estimates say 50 — 100 million people worldwide were killed . This pandemic has been described as " the greatest medical holocaust in history " and may have killed more people than the Black Death . As many as 17 million died in India , about 5 % of the population . In Japan , 23 million people were affected , and 390 , 000 died . In the U . S . , about 28 % of the population suffered , and 500 , 000 to 675 , 000 died . In Britain as many as 250 , 000 died ; in France more than 400 , 000 . In Canada 50 , 000 died . Entire villages perished in Alaska . In West Africa , an influenza epidemic killed at least 100 , 000 people in Ghana . In Dutch East Indies ( now Indonesia ) , 1 . 5 million assumed died from 30 million inhabitants . In Tahiti , 14 % of the population died during only two months . Similarly , in Samoa in November 1918 , 20 % of the population of 38 , 000 died within 2 months . Tafari Makonnen ( the future Haile Selassie ) was one of the first Ethiopia ns who contracted influenza but survived , although many of his subjects did not ; estimates for the fatalities in the capital city , Addis Ababa , range from 5 , 000 to 10 , 000 , or higher , while in British Somaliland one official estimated that 7 % of the native population died . This huge death toll was caused by an extremely high infection rate of up to 50 % and the extreme severity of the symptoms , suspected to be caused by cytokine storm s . Symptoms in 1918 were so unusual that initially influenza was misdiagnosed as dengue , cholera , or typhoid . One observer wrote , " One of the most striking of the complications was hemorrhage from mucous membranes , especially from the nose , stomach , and intestine . Bleeding from the ears and petechial hemorrhages in the skin also occurred . " The majority of deaths were from bacterial pneumonia , a secondary infection caused by influenza , but the virus also killed people directly , causing massive hemorrhages and edema in the lung . The unusually severe disease killed between 2 % and 20 % of those infected , as opposed to the usual flu epidemic mortality rate of 0 . 1 % . According to historian John M . Barry the most vulnerable of all , " those most likely , of the most likely " , to die , were pregnant women . He reported that in thirteen studies of hospitalized women in the pandemic , the death rate ranged from 23 % to 71 % . Of the pregnant women who survived childbirth over one quarter ( 26 % ) lost the child . Another unusual feature of this pandemic was that it mostly killed young adults , with 99 % of pandemic influenza deaths occurring in people under 65 , and more than half in young adults 20 to 40 years old . This is unusual since influenza is normally most deadly to the very young ( under age 2 ) and the very old ( over age 70 ) , and may have been due to partial protection caused by exposure to the previous Russian flu pandemic of 1889 . Modern analysis has shown the virus to be particularly deadly due to the fact it triggers a Cytokine Storm which ravages the stronger immune system of young adults . Patterns of fatality . Typical influenzas kill weak individuals , such as infant s ( aged 0 – 2 years ) , the elderly , and the immunocompromise d . Older adults may have had some immunity from the earlier Russian flu pandemic of 1889 . Another oddity was that the outbreak was widespread in the summer and autumn ( in the Northern Hemisphere ) ; influenza is usually worse in winter . In fast - progressing cases , mortality was primarily from pneumonia , by virus - induced pulmonary consolidation . Slower - progressing cases featured secondary bacterial pneumonias , and there may have been neural involvement that led to mental disorders in some cases . Some deaths resulted from malnourishment and even animal attacks in overwhelmed communities . Deadly second wave . The second wave of the 1918 pandemic was much deadlier 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 . But in August , when the second wave began in France , Sierra Leone and the United States , the virus had mutated to a much deadlier form . This has been attributed to the circumstances of the First World War . In civilian life evolutionary pressures favour a mild strain : those who get really sick stay home , and those mildly ill continue with their lives , go to work and go shopping , preferentially spreading the mild strain . In the trenches the evolutionary pressures were reversed : soldiers with a mild strain remained where they were , while the severely ill were sent on crowded trains to crowded field hospitals , spreading the deadlier virus . So the second wave began and the flu quickly spread around the world again . It was the same flu , in that most of those who recovered from first - wave infections were immune , but it was now far more deadly , and the most vulnerable people were those who were like the soldiers in the trenches — young , otherwise healthy adults . Consequently , during modern pandemics , health officials pay attention when the virus reaches places with social upheaval , looking for deadlier strains of the virus . This effect was most dramatically illustrated in Copenhagen , which escaped with combined mortality rate of just 0 . 29 % ( 0 . 02 % in first wave and 0 . 27 % in second wave ) because of exposure to the less lethal first wave . Devastated communities . Even in areas where mortality was low , so many were incapacitated that much of everyday life was hampered . Some communities closed all stores or required customers to leave orders outside . There were reports that the health - care workers could not tend the sick nor the gravediggers bury the dead because they too were ill . Mass graves were dug by steam shovel and bodies buried without coffins in many places . Several Pacific island territories were particularly hard - hit . The pandemic reached them from New Zealand , which was too slow to implement measures to prevent ships carrying the flu from leaving its ports . From New Zealand the flu reached Tonga ( killing 8 % of the population ) , Nauru ( 16 % ) and Fiji ( 5 % , 9 , 000 people ) . Worst affected was Western Samoa , a territory then under New Zealand military administration . A crippling 90 % of the population was infected ; 30 % of adult men , 22 % of adult women and 10 % of children were killed . By contrast , the flu was kept away from American Samoa when Governor John Martin Poyer imposed a blockade . In New Zealand itself 8 , 573 deaths were attributed to the 1918 pandemic influenza , resulting in a total population fatality rate of 7 . 4 per thousand ( 0 . 74 % ) . Less affected areas . In Japan , 257 , 363 deaths were attributed to influenza by July 1919 , giving an estimated 0 . 425 % mortality rate , much lower than nearly all other Asian countries for which data are available . The Japanese government severely restricted maritime travel to and from the home islands when the pandemic struck . In the Pacific , American Samoa and the French colony of New Caledonia also succeeded in preventing even a single death from influenza through effective quarantine s . In Australia , nearly 12 , 000 perished . End of the pandemic . After the lethal second wave struck in the autumn of 1918 , new cases dropped abruptly — almost to nothing after the peak in the second wave . In Philadelphia for example , 4 , 597 people died in the week ending October 16 , but by November 11 influenza had almost disappeared from the city . One explanation for the rapid decline of the lethality of the disease is that doctors simply got better at preventing and treating the pneumonia which developed after the victims had contracted the virus , although John Barry states in his book that researchers have found no evidence to support this . Another theory holds that the 1918 virus mutated extremely rapidly to a less lethal strain . This is a common occurrence with influenza viruses : there is a tendency for pathogenic viruses to become less lethal with time , providing more living hosts . Cultural and economic impact . In the United States , the United Kingdom and other countries , despite the relatively high morbidity and mortality rates that resulted from the epidemic in 1918 – 1919 , the Spanish flu began to fade from public awareness over the decades until the arrival of news about bird flu and other pandemics in the 1990s and 2000s . This has led some historians to label the Spanish flu a " forgotten pandemic " . There are various theories why the Spanish flu was " forgotten " . The rapid pace of the pandemic , which killed most of its victims in the United States , for example , within a period of less than nine months , resulted in limited media coverage . The general population was familiar with patterns of pandemic disease in the late 19th and early 20th centuries : typhoid , yellow fever , diphtheria , and cholera all occurred near the same time . These outbreaks probably lessened the significance of the influenza pandemic for the public . In some areas , the flu was not reported on , the only mention being that of ads for medicines claiming to cure it . In addition the outbreak coincided with the deaths and media focus on the First World War . Another explanation involves the age group affected by the disease . The majority of fatalities , from both the war and the epidemic , were among young adults . The deaths caused by the flu may have been overlooked due to the large numbers of deaths of young men in the war or as a result of injuries . When people read the obituaries , they saw the war or post - war deaths and the deaths from the influenza side by side . Particularly in Europe , where the war ' s toll was extremely high , the flu may not have had a great , separate , psychological impact , or may have seemed a mere " extension " of the war ' s tragedies . The duration of the pandemic and the war could have also played a role : the disease would usually only affect a certain area for a month before leaving , while the war , which most expected to end quickly , had lasted for four years by the time the pandemic struck . This left little time for the disease to have a significant impact on the economy . One final issue that the 1918 Spanish flu outbreak had on the world was the effects on the global economy . As could be expected , statistics show that many businesses in the entertainment and service industries suffered losses in revenue , but the health care industry reported profit gains . Spanish flu research . The origin of the Spanish flu pandemic , and the relationship between the near simultaneous outbreaks in humans and swine , have been controversial . One hypothesis is that the virus strain originated at Fort Riley , Kansas , in viruses in poultry and swine which the fort bred for food ; the soldiers were then sent from Fort Riley around the world , where they spread the disease . Similarities between a reconstruction of the virus and avian viruses , combined with the human pandemic preceding the first reports of influenza in swine , led researchers to conclude that the influenza virus jumped directly from birds to humans , and swine caught the disease from humans . Others have disagreed , and more recent research has suggested that the strain may have originated in a non - human mammalian species . An estimated date for its appearance in mammalian hosts has been put at the period 1882 – 1913 . This ancestor virus diverged about 1913 – 1915 into two clade s which gave rise to the classical swine and human H1N1 influenza lineages . The last common ancestor of human strains dates to between February 1917 and April 1918 . Because pigs are more readily infected with avian influenza viruses than are humans , it is suggested that they were the original recipient of the virus , passing the virus to humans sometime between 1913 and 1918 . An effort to recreate the 1918 flu strain ( a subtype of avian strain H1N1 ) was a collaboration among the Armed Forces Institute of Pathology , Southeast Poultry Research Laboratory and Mount Sinai School of Medicine in New York City ; the effort resulted in the announcement ( on October 5 , 2005 ) that the group had successfully determined the virus ' s genetic sequence , using historic tissue samples recovered by pathologist Johan Hultin from a female flu victim buried in the Alaskan permafrost and samples preserved from American soldiers . On January 18 , 2007 , Kobasa et al . reported that monkeys ( Macaca fascicularis ) infected with the recreated strain exhibited classic symptoms of the 1918 pandemic and died from a cytokine storm — an overreaction of the immune system . This may explain why the 1918 flu had its surprising effect on younger , healthier people , as a person with a stronger immune system would potentially have a stronger overreaction . On September 16 , 2008 , the body of Yorkshire man Sir Mark Sykes was exhumed to study the RNA of the Spanish flu virus in efforts to understand the genetic structure of modern H5N1 bird flu . Sykes had been buried in 1919 in a lead coffin which scientists hope will have helped preserve the virus . In December 2008 , research by Yoshihiro Kawaoka of the University of Wisconsin linked the presence of three specific genes ( termed PA , PB1 , and PB2 ) and a nucleoprotein derived from 1918 flu samples to the ability of the flu virus to invade the lungs and cause pneumonia . The combination triggered similar symptoms in animal testing . In June 2010 , a team at the Mount Sinai School of Medicine reported that the 2009 flu pandemic vaccine provided some cross - protection against the 1918 flu pandemic strain .