Australia, being in the Southern Hemisphere, has already had winter.
The influenza season Down Under was particularly brutal with a record-high number of flu cases. The main culprit was the influenza A (H3N2) strain. The Aussies’ flu vaccine, which has the same components as ours, was only 10% effective against this strain.
There are reasons why the yearly influenza vaccine is not as effective as most other vaccines.
Because the types of flu viruses circulating during any given flu season can change, the influenza vaccine is made specifically for each flu season. In addition, both main types of influenza viruses (A and B) have multiple strains that differ enough that immunity to one strain usually does not give you immunity to another.
Influenza strains also have a habit of mutating. They can combine with other influenza viruses in certain animals.
The World Health Organization, with input from the CDC, usually decides by the February before the next flu season what components to put in the influenza vaccine.
Two of the likely influenza A strains and one or two of the likely influenza B strains that are likely to be circulating are grown, usually in chicken eggs, and then manufactured into vaccine. This process takes at least six months.
In other words, the vaccine is based on an educated guess.
The influenza A strains that are grown in chicken eggs to make the flu vaccine will often mutate to the point where they will not trigger as much immunity against the original, formerly identical, circulating strains.
This is thought to decrease the yearly influenza vaccine’s efficacy by about 10%.
A way around this could possibly be to grow the strains used in the influenza vaccine in mammalian cell cultures.
Even in a flu season where the WHO and CDC guess the correct strains to use, the efficacy of the influenza vaccine is only 40-60%.
Ideally, the best solution would be to devise a universal influenza vaccine that would give good and lasting immunity against all strains of both types of influenza.
This is proving extremely difficult given the influenza virus’ ability to mutate and recombine.
Despite the obstacles, the CDC estimates that between the 2005-2006 and 2013-2014 seasons 40,000 deaths were prevented by the vaccine.
Therefore, the CDC still recommends that those six months of age and above get vaccinated yearly against influenza.