Understanding Flu Viruses
Influenza (Flu) Viruses
There are two main types of human flu viruses: types A and B. The flu A and B viruses that routinely spread in people are responsible for seasonal flu epidemics each year.
Flu 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 (flu A) of flu circulate and cause illness.
More Information about Flu Viruses
- Types of Flu Viruses
Flu A and B viruses are responsible for seasonal flu epidemics more commonly known as the flu season.
- How Flu Viruses Can Change
Flu viruses can change in two different ways—antigenic drift and antigenic shift.
- Transmission of Flu Viruses from Animals to People
Flu A viruses also are found in many different animals, including ducks, chickens, pigs, horses, whales, and seals.
- Pandemic Flu
A flu pandemic is a global outbreak of a new flu A virus. Learn more, including about past flu pandemics.
- Images of Flu Viruses
Graphics of generic flu viruses
- Human Serology and Flu
CDC conducts human serology work to improve seasonal flu vaccines and prepare against future flu pandemics.
- Antigenic Characterization of Flu Viruses
CDC antigenically characterizes circulating flu viruses each year to monitor for changes and to help inform flu vaccine composition recommendations.
- Flu Virus Genome Sequencing and Genetic Characterization
CDC studies genetic changes in circulating flu viruses to support public health objectives.
- Advanced Molecular Detection (AMD) and Flu
CDC’s Advanced Molecular Detection (AMD) initiative uses new technology to study flu viruses faster and in more detail than ever before.
Related Questions & Answers
- Seasonal Flu, More Information
- Flu-Related Questions & Answers by Topic
- Reconstruction of the 1918 Flu Pandemic Virus