Influenza (Flu) Viruses
There are two main types of influenza (flu) virus: Types A and B. The influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal flu epidemics each year. Influenza A viruses can be broken down into sub-types depending on the genes that make up the surface proteins. Over the course of a flu season, different types (A & B) and subtypes (influenza A) of influenza circulate and cause illness.
More Information about Flu Viruses
- Types of Influenza Viruses
Influenza A and B viruses are responsible for seasonal flu epidemics each year. - How the Flu Virus Can Change
Influenza viruses can change in two different ways—antigenic drift and antigenic shift. - Images of Influenza Viruses
Graphics of generic influenza viruses - Transmission of Influenza Viruses from Animals to People
Influenza A viruses also are found in many different animals, including ducks, chickens, pigs, whales, horses and seals. - 2009 H1N1 Influenza
The influenza A (H1N1) virus that emerged in 2009 caused the first global influenza pandemic in more than 40 years.
Questions & Answers about Flu Viruses
- Influenza (Flu) Research
Information about CDC’s past and current research on influenza viruses
Contact Us:
- Centers for Disease Control and Prevention
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TTY: (888) 232-6348 - cdcinfo@cdc.gov