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Influenza (vaccine-preventable)

Disease Information

Influenza, commonly known as the flu, is a contagious respiratory tract infection caused by the influenza virus. Symptoms of influenza generally include fever, cough, sore throat, muscle aches, headache, or fatigue. Influenza can cause mild to severe illness, and at times can lead to death.

During most influenza seasons, typically from November to April, between 10 percent and 20 percent of the population is infected with influenza. More than 200,000 people are hospitalized with influenza each year in the U.S. Certain groups of people, including older adults, young children, pregnant women, and people with certain health conditions, are at higher risk for serious complications from influenza illness.

The best way to avoid getting and spreading the flu is by getting vaccinated each year. Get more information on influenza prevention, treatment, and find out where to get a flu shot at

Disease Reporting

Reporting Requirements for Seasonal and Novel Influenza


Investigative Guidelines

Novel Influenza

Influenza viruses constantly change and mutate. Novel strains of influenza A virus can cause severe illness in humans. These influenza viruses are different from currently circulating human influenza A virus subtypes and include influenza viruses from predominantly avian and swine origin. In recent years, human infections with highly pathogenic influenza A (H1N1, H5N1, H7N3, and H7N9), and variant influenza A (H3N2v and H1N2v) viruses have been reported.


See Also

For parents

For healthcare and public health professionals

CDC Factsheet