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An electron microscope image shows an A H1N1 "swine flu" virus culture obtained from a California patient suffering from the international flu outbreak - Source: Reuters -
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There were three widespread influenza pandemics in the 20th century.
- The first, in 1918-1919, killed between 50 million and 100 million people. It is now known to have been caused by an H1N1 strain of the virus.
- The second in 1957 was caused by a strain called H2N2 and was known as Asian flu. It came in several waves of varying severity between 1957 and 1960.
- A third pandemic in 1968, called Hong Kong flu, occurred in waves and was caused by the H3N2 strain.
- Experts believe that the current strain of H1N1 swine flu may follow the same pattern and that the relatively mild symptoms now seen in most patients become more severe in future cases.
- A key concern is that it may mix with widespread Tamiflu-resistant forms of H1N1 seasonal flu.
- Because the H1NI flu is new, human immune systems will not immediately recognise the virus, and the proportion of the population falling ill is likely to be far higher than happens with seasonal flu, which hits up to 20% of the nation.
- New Zealand health officials say that every week they can delay widespread community transmission of the virus is another week they can avoid overloading medical staff already faced with an average 156,000 seasonal flu patients each winter.
- Tamiflu and another retroviral treatment, Relenza, are the main medical weapons to battle pandemic H1N1 flu. The government has emergency stocks of 1.25 million doses of Tamiflu, and has ordered 125,000 doses of Relenza, enough to reduce the symptoms in about a third of the population.
