The Influenza (Flu) Viruses

There are two main types of influenza (flu) virus: Types A and B. Influenza A and B viruses that routinely spread in people (human influenza viruses) are responsible for seasonal flu epidemics each year. The emergence of a new influenza virus causing illness in people can result in an influenza pandemic, as occurred in the spring of 2009 when a new influenza A (H1N1) virus emerged to cause illness in people and spread worldwide.

Influenza A viruses can be broken down into sub-types. Over the course of a flu season, different types (A & B) and subtypes of influenza A viruses can circulate and cause illness. In addition, influenza viruses are constantly changing through a process called "antigenic drift."

• Types of Influenza Viruses
  Influenza A and B viruses are responsible for seasonal flu epidemics each year a?|
• How the Flu Virus Can Change
  Influenza viruses can change in two different ways a?|
• Influenza in Animals
  Influenza A viruses are found in many different animals, including ducks, chickens, pigs, whales, horses and sealsa?|
• 2009 H1N1 Influenza

Questions & Answers

• Research