Influenza

Influenza, also known as flu, is a contagious viral respiratory infection caused by influenza viruses. It can cause mild to severe illness and, in some cases, can be serious and even fatal.

Seasonal influenza strikes every year and affects 5% to 20% of the U.S. population annually. In the U.S. alone, annual deaths caused by flu range from 6,300 to 52,000 people, and 120,000 to 710,000 people are hospitalized each year. During the 2024-2025 flu season, there were 280 pediatric flu deaths in the U.S., the highest number of child deaths reported since 2004, expect for during the 2009-2010 H1N1 flu pandemic.

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Symptoms and Treatment

Flu can cause fever, muscle or body aches, headaches, fatigue, coughing, sore throat, congestion and a runny nose. People who have flu often feel some or all of these symptoms. Some people may have vomiting and diarrhea, though this is more common in children than adults.

Antiviral treatment can lessen the symptoms and shorten the duration of the flu, especially if taken within 48 hours of symptoms beginning. Antiviral treatment can also help reduce flu complications in people who are at higher risk for severe illness.

People who are more likely to get very sick include children under 5, adults over 65 or people with certain medical conditions, such as chronic lung disease, heart disease or a weakened immune system.

Prevention

There are several core prevention strategies that everyone can use to help protect themselves and others from respiratory viruses, including influenza. These include good hygiene (covering your coughs and sneezes, washing or sanitizing your hands often and cleaning frequently touched surfaces), taking steps for cleaner air and staying home when sick.

The best way to prevent influenza is by getting a flu vaccine every year, ideally in September or October, before the beginning of flu season. The flu vaccine is recommended for everyone ages 6 months and older. Flu vaccination has been shown to reduce the risk of flu illnesses, hospitalizations and flu-related deaths. See your health care provider or find a flu vaccination location near you.

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Bird flu

Avian influenza A(H5N1), also known as highly pathogenic avian influenza or bird flu, is a disease caused by infection with avian influenza type A viruses. Bird flu is widespread in wild birds and is causing outbreaks in poultry and other animals and sporadic cases in people. Learn more about bird flu, which is caused by different viruses than those that cause seasonal flu in humans.