Spanish flu

Spanish flu
Soldiers sick with Spanish flu at a hospital ward at Camp Funston in Fort Riley, Kansas
Disease	Influenza
Virus strain	Strains of A/H1N1
Location	Worldwide
First outbreak	Unknown
Date	February 1918 – April 1920[1]
Suspected cases‡	500 million (estimated)[2]
Deaths	25–50 million (generally accepted), other estimates range from 17 to 100 million[3][4][5]
‡Suspected cases have not been confirmed by laboratory tests as being due to this strain, although some other strains may have been ruled out.

Influenza (flu)
Types Avian A/H5N1 subtype Canine Equine Swine A/H1N1 subtype
Vaccines 2009 pandemic Pandemrix Live attenuated Seasonal flu vaccine brands
Treatment Amantadine Baloxavir marboxil Laninamivir Oseltamivir Peramivir Rimantadine Umifenovir Zanamivir
Pandemics 1889-1890 Russian flu 1918 Spanish flu 1957-1958 Asian flu 1968 Hong Kong flu 1977 Russian flu 2009 swine flu
Outbreaks 1976 swine flu 2006 H5N1 India 2007 Australian equine 2007 Bernard Matthews H5N1 2008 West Bengal 2015 United States H5N2 outbreak 2020–2022 H5N8 outbreak
See also Flu season Influenza evolution Influenza research Influenza-like illness Vaccine reformulations
v t e

The 1918–1920 flu pandemic, also known as the Great Influenza epidemic or by the common misnomer Spanish flu, was an exceptionally deadly global influenza pandemic caused by the H1N1 influenza A virus. The earliest documented case was March 1918 in the state of Kansas in the United States, with further cases recorded in France, Germany and the United Kingdom in April. Two years later, nearly a third of the global population, or an estimated 500 million people, had been infected in four successive waves. Estimates of deaths range from 17 million to 50 million,^[6] and possibly as high as 100 million, making it one of the deadliest pandemics in history.

The pandemic broke out near the end of World War I, when wartime censors in the belligerent countries suppressed bad news to maintain morale, but newspapers freely reported the outbreak in neutral Spain, creating a false impression of Spain as the epicenter and leading to the "Spanish flu" misnomer.^[7] Limited historical epidemiological data make the pandemic's geographic origin indeterminate, with competing hypotheses on the initial spread.^[2]

Most influenza outbreaks disproportionately kill the young and old, with a higher survival rate in-between, but this pandemic had unusually high mortality for young adults.^[8] Scientists offer several explanations for the high mortality, including a six-year climate anomaly affecting migration of disease vectors with increased likelihood of spread through bodies of water.^[9] The virus was particularly deadly because it triggered a cytokine storm, ravaging the stronger immune system of young adults,^[10] although the viral infection was apparently no more aggressive than previous influenza strains.^[11][12] However, the claim that young adults had a high mortality during the pandemic has been contested.^[13] Malnourishment, overcrowded medical camps and hospitals, and poor hygiene, exacerbated by the war, promoted bacterial superinfection, killing most of the victims after a typically prolonged death bed.^[14][15]

The 1918 Spanish flu was the first of three flu pandemics caused by H1N1 influenza A virus; the most recent one was the 2009 swine flu pandemic.^[16][17] The 1977 Russian flu was also caused by H1N1 virus.^[16][18]