This year’s flu season has been the worst in many decades, with 85 deaths since the beginning of winter. Media has blamed the ‘Aussie flu’, but it isn’t as simple as one type of flu.
This is because the flu isn’t just one virus. It is a group of four closely related viruses, made up of influenza A, B, C and D. Humans cannot get influenza D, but we can get infected by the rest. Most hospitalizations and deaths are caused by types A and B.
There are many types of influenza type A, but only two types of influenza B. Type A is found in many animals, such as pigs and birds. The major worry in health care is that a new virus will jump from infecting animals to being able to infect humans. This would be a major issue as humans would not have had a chance to build up an immunity to the strain, but this is not what has happened this year.
The main reason why the flu has been so bad is that the most common strain of flu this year is difficult to control. This strain of influenza A, H3N2, is the flu that caused Australia’s terrible flu season. H3N2 tends to cause more hospitalisations and death in older people and is hard to vaccinate effectively against. Another issue with this year’s flu is that the usually more uncommon strain of influenza B has been more common. The vaccine does not protect against this strain. Also, the vaccine this year showed to be only 20 per cent effective against the H3N2 strain.
This low percentage of protection against H3N2 is due the way flu vaccines are made. Flu viruses are grown inside chicken eggs and then inactivated before being used in vaccines. Flu viruses have a high mutation rate, and these mutations are specific to their environment. Because a chicken egg is a very different environment to a human body, sometimes the end result may be a virus which does not give a good vaccine. That is what happened this year.
The flu vaccines need to be remade each year because of the rate that flu viruses mutate. Viruses attack the cells in your body by first attaching to the cell surface using specific proteins. Your immune system protects you from viruses by making antibodies, which fit perfectly to these proteins. Your immune system will then remember the shape of these antibodies and can quickly recreate these antibodies if you get the flu again, which prevent the illness.
A vaccine puts an inactive virus into your body. Your immune system then reacts in the usual way, except because the virus is inactive you do not get ill, but your body remembers the virus, so it can quickly attack if the real virus invades your body.
Every time a virus mutates the old vaccine will not work, as the proteins change. So, every year scientists rush to make a new vaccine before the flu season starts.
Scientists are working on creating a vaccine that will work against any strain. But for now, defend yourself by getting a vaccine if you are in an at risk group, maintaining good personal health, and if you do get ill, avoid crowded places!