The British media have blamed “Aussie flu” for the outbreak. The truth is, there is not just one flu strain we should be worried about, and “Aussie flu” is a bit of a misnomer.
First, a bit about flu strains. There isn’t really a flu virus. Flu virus is a name we give a group of four closely related viruses: influenza A, influenza B, influenza C and influenza D. While humans can’t catch influenza D (that’s for pigs and cows), we can be infected with influenza A, B and C. Public health officials, however, are less worried about influenza C as it isn’t a major cause of illness. But influenza A and B are a real worry.
Influenza A has been found in – and causes disease in – lots of animals, including birds, bats, dogs, pigs and penguins. One of the major worries is pandemic influenza, where a new virus jumps from animals and spreads across the world easily because we haven’t had a chance to build up immunity to that new type.
Influenzas A and B can be subdivided even further by the proteins they carry on their surface – hemagglutinin (H) and neuraminidase (N). These proteins help the virus identify the right cells to infect.
For influenza A there are 18 Hs and 11 Ns identified so far. Hence we get names such as H1N1 for swine flu or H5N1 for bird flu. Contrast this with the fact that there are really only two lineages of influenza B, named after cities in Japan and Australia: Yamagata and Victoria, respectively.
The Hs and Ns are continuously evolving in response to our immune systems, which recognise and make antibodies to stop the virus taking hold. A vaccine usually supplies the H and N proteins without the potentially dangerous virus. Scientists also continuously track the H and N of circulating influenza viruses and adjust the vaccine to match what’s out there. This is the basis for flu vaccination and why you have to get a new vaccine jab every year.