Influenza (Flu)

Flu activity has returned to summer-time levels in the United States. H3N2 viruses were most common overall during this season, however, there was a wave of influenza B activity starting in early March. According to a report published in the Morbidity and Mortality Weekly Report (MMWR), the season was moderately severe overall, and severe for people 65 years and older, with very high hospitalization rates in that age group.

While most flu activity occurs from October to May in the United States, flu viruses are detected year-round, including at lower levels during the summer months. Influenza antiviral drugs can treat flu illness. CDC recommends these drugs be used to treat people who are very sick or who are at high risk of serious flu-related complications who have flu symptoms. Early antiviral treatment works best.

There are many different influenza A viruses; some are found in humans and others in animals such as avian flu in birds and poultry.

U.S. H5 Viruses: Highly pathogenic avian influenza (HPAI) H5 infections have been reported in U.S. birds and poultry. No human infections with these viruses have been detected at this time, however similar viruses have infected people in other countries and caused serious illness and death in some cases.

Influenza viruses that normally circulate in pigs are called “variant” viruses when they are found in people. Influenza A H3N2 variant viruses (also known as “H3N2v” viruses) with the matrix (M) gene from the 2009 H1N1 pandemic virus were first detected in people in July 2011.

There are many different influenza A viruses; some are found in humans and others in animals such as swine flu in pigs.

CDC’s pandemic preparedness efforts include ongoing surveillance of human and animal influenza viruses, risk assessments of influenza viruses with pandemic potential, and the development and improvement of preparedness tools that can aid public health practitioners in the event of an influenza pandemic.

Bat influenza refers to influenza A viruses found in bats. Laboratory research at CDC suggests these viruses would need to undergo significant changes to become capable of infecting and spreading easily among humans. Little yellow shouldered bats are not native to the continental United States, but are common in Central and South America.

Dog flu is a contagious respiratory disease in dogs caused by a specific Type A influenza virus referred to as a “canine influenza virus.” This is a disease of dogs, not of humans.

Influenza A viruses are found in humans and many different animals, including ducks, chickens, pigs, whales, horses and seals. Additional information on 2009 H1N1 influenza, Flu.gov, and Nonpharmaceutical Interventions (NPIs).

Flu Activity & Surveillance

Check where flu is active near you.

International Flu

Fiscal Years 2012 and 2013, Annual Report, Influenza Division International Activities The latest report on CDC's international flu activities highlights the progress that has been made over the past two fiscal years in establishing, expanding and maintaining influenza surveillance and laboratory capacity in more than 50 countries around the world where CDC has provided support.