Class A flu is more accurately known as influenza A. It refers to influenza viruses of the A type, which are the only influenza viruses known to cause flu pandemics, meaning global epidemics of flu disease.
Understanding Influenza A
Influenza A viruses are distinct because they can infect humans and a variety of animals, including birds, pigs, horses, and other mammals. This ability to cross species boundaries is a key factor in the emergence of novel influenza strains.
Why Influenza A Causes Pandemics
The potential for pandemics arises when a new influenza A virus emerges that:
- Infects humans.
- Spreads easily from person to person.
- Evades existing immunity in the human population.
Examples of Influenza A Viruses
Examples of influenza A subtypes that have caused pandemics include:
- H1N1: The cause of the 1918 Spanish Flu pandemic and the 2009 Swine Flu pandemic.
- H2N2: The cause of the 1957 Asian Flu pandemic.
- H3N2: The cause of the 1968 Hong Kong Flu pandemic.
Influenza A vs. Other Influenza Types
There are other types of influenza viruses (B, C, and D), but influenza A stands out because of its pandemic potential. Influenza B can also cause epidemics, but generally causes milder disease than influenza A. Influenza C typically causes mild illness, and influenza D primarily affects cattle.
In summary, influenza A viruses are the influenza viruses most likely to cause widespread and severe disease outbreaks because of their ability to infect multiple species and rapidly evolve.
