A, B and C are the three main types flu virus family contains. Flu viruses are known to mutate (change) over time. Also, strains of the flu virus are classified on where and when they were first identified and given a serial number.
Flu A More frequently occurs (every two to three years) and is more serious than type B. It is very likely to transform and it commonly produces varieties to which populations have no resistance. It is for this reason that widespread epidemics occur that may affect whole continents. These are known as pandemics and are caused by new strains of the type A virus.
flu B Generally, causes a less severe illness, although it is responsible for smaller outbreaks. Than the flu A virus Flu B is much more stable and if you have been infected with flu B, your immunity to further flu B infections will last for many years. Flu B mainly affects young children (5-14 years of age) who have not been exposed to the virus and have not developed immunity.
In the winter of 2005/6, the majority of flu activity was confined to type B with only a few cases of flu A reported. Type C usually causes a mild illness similar to the common cold.
In recent years, two subtypes of flu A have been circulating, the H1N1 subtype and the H3N2 subtype – Panama or Moscow-like strains. In 2003/4, the main strain circulating was a flu A (H3N2) Fujian-like strain.
