The 1918 Pandemic

The 1918 virus (H1N1) is inappropriately called the "Spanish Flu" as it most likely originated in the USA [in January 1918, Haskell County, Kansas according to JM Barry in "The Great Influenza. Penguin, 2005"] .

The parent viruses may have been circulating for several years, accumulating the necessary changes to become adapted to humans.

For further information refer to: The origins of pandemic influenza - "Lessons from the 1918 virus" by Belshe R.B New England Journal of Medicine 353:2209 - 2211 Nov 24 2005

Refs: Reid AH, Fanning TG, Janczewski TA, Lourens RM, Taubenberger JK. Novel origin of the 1918 pandemic influenza virus nucleoprotein gene. J Virol. 2004 Nov;78(22):12462-70. Reid AH, Taubenberger JK, Fanning TG. Evidence of an absence: The genetic origins of the 1918 pandemic influenza virus. Nat Rev Microbiol 2004 Nov; 2(11): 909-14.

Recent genetic analysis of the 1918 virus shows that it emerged by direct mutation from an avian influenza virus.

Ref: Taubenberger JK, Reid AH, Lourens RM, Wang R, Jin G, Fanning TG. Characterization of the 1918 influenza virus polymerase genes. Nature. 2005 Oct 6;437(7060):889-93.

Wordwide Impact:

The 1918 pandemic caused an unknown number of deaths. The estimate of 50 million comes from the most recent assessment that noted the figure could still be a substantial underestimate and speculated that the total might be double at 100 million deaths.

Ref: Johnson NP, Mueller J. Updating the accounts: Global mortality of the 1918--1920 "Spanish" influenza pandemic. Bull Hist Med 2002; 76(1): 105-15.

Emergency hospital during influenza epidemic, Camp Funston, Kansas. 1918 epidemic sourced from the National Museum of Health and Medicine, Washington DC http://nmhm.washingtondc.museum

The 1918 pandemic killed around 20% of Western Samoa's population. Of note, neighbouring American Samoa was spared by implementing an effective quarantine policy. New Zealand failed in its attempt at a quarantine, partly because the virus arrive in New Zealand relatively early (Jun 1918) - in contrast Australia instituted a vigorous quarantine programme and as a result the virus did not arrive in Australia till around Jan 1919.

NZ Impact:

The 1918 pandemic affected somewhere between a third and a half of the entire New Zealand population and caused an estimated 8250 deaths (0.74% of the population). It was particularly severe on Maori with 2160 of all deaths being in Maori!

Influenza Depot, 4 Dec 1918, reference number: 1/1-008542-G.
Alexander Turnbull Library, Wellington.

Below a nurse leaving a sub-depot on her daily round of visits, during the 1918 influenza epidemic, Christchurch

Disproportionate burden in young adults:

The dramatic impact of the 1918 virus can be seen in USA data showing how it reduced life-expectancy (by 13 years) - an effect not seen with the 1957 and 1968 pandemics. USA data also show the disproportionate impact on those aged 20-40 years - the "W" mortality curve; this was not seen in subsequent pandemics. The 1918 impact also caused increases in deaths in children, but in relative terms this was not as dramatic as the effect seen in young adults.

The reason for the disproportionate impact of the 1918 pandemic on young adults is not known.