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Types of Influenza Viruses

There are three types of flu virus: influenza A, B and C. Each virus has similar symptoms and infects your lungs and upper airways, causing a sudden high temperature and general aches and pains. Typically, every year, there will be one or two strains of influenza A circulating, as well as a single type B strain. Not all of the strains are equally dangerous and equally widespread, with influenza A and B being the most common.

Anatomy of a Flu Virus
Flu virus anatomy

Influenza A

Influenza A has the potential to be the most dangerous and harmful of all three types of the flu virus. Predominately found in wild birds, strain A can and has been transmitted between different animal species, including humans. When it is transmitted, the strain is changed and the virus can evolve without warning. When this occurs, coupled with the fact that influenza is a highly contagious virus, pandemics and mass outbreaks of type A can occur. Swine flu and bird flu are both examples of type A that have evolved through the species to result in a potentially deadly virus.

These viruses can also be divided into further subtypes dependent on the types of proteins present on their surface, namely hemagglutinin (H) and neuraminidase (N). For example, swine flu is also known as H1N1 and bird flu is known as H5N1.

Influenza B

Influenza B is most commonly found in humans. It is the simplest type of flu you can get, in the sense that it does not have a strong ability to mutate or evolve, making the virus stable. Because the virus remains the same, a cure has been created and people suffering from it can be treated relatively easily and effectively. Strain B mutates up to three times slower than the likes of A, and because of this, humans are able to also develop immunity to it from a younger age.

Influenza C

Type C is the least common type of influenza and can be found in dogs, pigs and humans. It seldom actually infects adults, but it can infect young children. It does not spark epidemics but can cause respiratory infections and complications if a person is infected.

Influenza A Influenza B Influenza C
Most dangerous
Least dangerous  
Most common  
Least common  
Causes most pandemics  
Least likely to cause pandemics  
More common in children than adults  
Strong ability to mutate and evolve into more dangerous strains  

What are the most dangerous strains of flu?

Type A is the only type of flu that is life threatening. The reason for this is that the subtypes it mutates into can occur without warning. These subtypes, such as swine flu and bird flu, which can attack humans, are brand new strains of the virus for which there are no readily available treatments. The time it takes to develop new treatments therefore allows for the spread of the new subtype, which is how pandemics are started. The subtype spreads rapidly and infects a lot of people. Until a cure is found or the spread is under control, the influenza virus can cause many fatalities, especially in areas where people don’t have access to sufficient treatment.

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