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The flu (influenza) is a very contagious viral infection of the respiratory tract.

More to Know

Flu viruses usually cause the most illness during the colder months of the year. Sometimes the flu is confused with a cold, but flu symptoms come on suddenly and can be more severe.

Flu symptoms include a fever, sore throat, headache, cough, weakness, muscle pains, and loss of appetite. Fever and other symptoms usually end after about a week, but coughing and weakness may go on for longer.

To cope with symptoms, drink lots of liquids, get plenty of rest, and take acetaminophen or ibuprofen to relieve fever and aches.

Sometimes, the flu is a serious illness, and can lead to pneumonia, dehydration, and other life-threatening problems. Infants, seniors, and people with long-term health problems are at the highest risk for serious problems from the flu.

Keep in Mind

You can help protect your family from the flu by getting the flu vaccine every year. Everyone 6 months of age and older should get vaccinated at the start of each flu season.

All A to Z dictionary entries are regularly reviewed by KidsHealth medical experts.