18/04/2026
Influenza
Flu, also called influenza, is an infection of the nose, throat and lungs, which are part of the respiratory system. The flu is caused by a virus. Influenza viruses are different from the "stomach flu" viruses that cause diarrhea and vomiting.
Most people with the flu get better on their own. But sometimes, influenza and its complications can be deadly. To help protect against seasonal flu, you can get an annual flu shot. Although the vaccine isn't 100% effective, it lowers the chances of having severe complications from the flu. This is especially true for people who are at high risk of flu complications.
Symptoms
The viruses that cause flu spread at high levels during certain times of the year in the Northern and Southern hemispheres. These are called flu seasons. In North America, flu season usually runs between October and May.
Symptoms of the flu such as a sore throat and a runny or stuffy nose are common. You may also get these symptoms with other illness such as a cold. But colds tend to start slowly, and the flu tends to come on quickly, within two or three days after you come in contact with the virus. And while a cold can be miserable, you usually feel much worse with the flu.
Other common flu symptoms include:
Fever.
Cough.
Headache.
Muscle aches.
Feeling very tired.
Sweating and chills.