In the twentieth century, the world experienced three influenza pandemics:
1918The Spanish flu swept across the world in three waves between 1918 and 1919. It tended to affect an area for up to 12 weeks and then would suddenly disappear, almost as quickly as it had arrived, only to return several months later. This wave pattern matches descriptions of some earlier pandemics, and occurred in a less pronounced form in the milder pandemics of 1957-58 and 1968-70.
In terms of the loss of human lives, the Spanish flu was unprecedented in modern times. More people died during the pandemic than were killed in the First World War. The illness came on suddenly and progressed rapidly to respiratory failure and in some instances death. Many people died from bacterial disease after infection with influenza (known as secondary bacterial infection).
Worldwide, at least 50 million people are thought to have died, with unusually high numbers of deaths in young and healthy people aged 15 to 35 years. It has been estimated that about 25 per cent of the world’s population was infected. Global spread and severity were influenced by the war and the movement of troops.
The Spanish flu did not reach Australia until 1919, partly because of strict maritime quarantine implemented by the government. It began in Victoria, spread to New South Wales then to the rest of Australia. By the end of 1919 (when the Australian population was just over 5 million), around 10,000 Australians, mostly young adults, had died of influenza. As in other countries, health services in Australia were greatly stretched during this time.
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1957The influenza pandemic of 1957-58 was called the Asian flu. Although the proportion of people infected was high, the illness was relatively mild compared to the Spanish flu, resulting in milder effects and fewer deaths. The first wave of the pandemic was concentrated in school-children and the second in the elderly. Infants and the elderly were more likely to die. It is estimated that the Asian flu caused two million deaths worldwide.
Studies show that the virus responsible for this pandemic arose by genetic reassortment of a bird virus.
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1968The 1968-70 pandemic or Hong Kong flu was also relatively mild compared to the Spanish flu. It affected mainly the elderly and is thought to have caused about one million deaths worldwide.
Studies show that the virus responsible for this pandemic arose by genetic reassortment.
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2009A new H1N1 influenza virus derived from human, swine and avian strains was initially reported in April 2009 in Mexico and subsequently spread around the world. Cases of pandemic (H1N1) influenza 2009 have been confirmed in most other countries throughout the world by the World Health Organization.
The pandemic (H1N1) influenza 2009 virus is not the same as seasonal influenza. The virus is mild in most people. However, in a small proportion of people the virus causes death due to viral pneumonia and lung failure. High risk groups have been identified where the illness is more likely to cause complications, including patients with chronic respiratory conditions, pregnant women, patients who are obese (BMI >30), indigenous people and patients with chronic cardiac, neurological and immune conditions. Children and younger people have also been shown to be at increased risk of serious complications as well as rapid spreaders of the virus.
In Australia during 2009, there were 37,636 cases of pandemic (H1N1) influenza 2009, including 191 associated deaths. The median age of those dying was 53 years, compared to 83 years for seasonal influenza.
For further information refer to the Pandemic (H1N1) Influenza 2009 page.