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There were three influenza pandemics during the 20th century:
- Spanish flu (H1N1) swept across the world in three waves in 1918 and 1919. It caused an estimated 50 million deaths worldwide (1–2% of the global population) and approximately 10,000 Australians died. The highest number of deaths was in young and healthy people aged 15–35 years; pregnant women were especially vulnerable.
- Asian flu (H2N2) in 1957 caused approximately 2 million deaths worldwide. During the first wave, school children, young adults and pregnant women were mainly affected. In the second wave, the elderly had the highest death rates.
- Hong Kong flu (H3N2) occurred in 1968 and 1969 and caused approximately 1 million deaths worldwide. It mainly affected the elderly.
Along with millions of deaths, these influenza pandemics caused social disruption and profound economic losses worldwide.
The first influenza pandemic this century was in 2009; it was referred to as ‘swine flu’ (H1N1). The virus contained genetic material of swine, avian and human origin.18 The virus has also been isolated in turkeys, cats and domestic ferrets.19 While the infection rate was high, there was a comparatively low mortality rate (18,449 laboratory-confirmed deaths as of 31 August 2010 by the WHO).
However, laboratory-confirmed deaths greatly underestimate the real mortality burden; for example, deaths from secondary bacterial infections and exacerbation of pre-existing chronic conditions are not recorded as being in any way related to influenza infection.8
Global mortality estimates by the Global Pandemic Mortality project suggest that there were between 123,000 and 203,000 pandemic respiratory deaths for the last 9 months of 2009 (which is approximately 10-fold higher than the WHO mortality count). The majority (62–85%) were attributed to persons under 65 years of age.8