What Is Influenza?
1. What Are the Different Types of Influenza?
There are four main types of influenza, with many different subtypes. The four types are: A, B, C and D. Only influenza A and B are known to cause seasonal epidemics. Influenza C rarely affects humans and typically causes mild cases, while influenza D primarily infects cattle.
Each main type is then further classified into subtypes and given an H and N number such as H1N1 or H3N2. The infection rate, severity and other factors vary depending on the subtype of the flu. Understanding subtypes is critical to developing a vaccine and preventing further serious cases.
