Flu Influenza, also known as the flu, is a viral infection that affects the respiratory system (nose, throat, and lungs). The flu can be caused by various types of influenza viruses, including influenza A, B, and C. The most common types of flu that affect humans are influenza A and B.

Symptoms of the flu typically include fever, chills, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, and sometimes vomiting and diarrhea, although these symptoms are more common in children. Some people may have mild symptoms and may not realize that they have the flu, while others may develop serious complications such as pneumonia.

There are several types of influenza A viruses, which are classified based on the surface proteins called hemagglutinin (H) and neuraminidase (N).

There are 18 different types of hemagglutinin and 11 types of neuraminidase, and different combinations of these proteins can result in different subtypes of influenza A viruses.

Influenza B viruses are less common than influenza A and are usually less severe, although they can still cause serious illness. Influenza C viruses are the least common and generally cause mild illness.

The flu is highly contagious and is spread through respiratory droplets that are released when an infected person talks, coughs, or sneezes. The flu can also be spread by touching a surface or object that has the virus on it and then touching one’s mouth, nose, or eyes.

It is possible to reduce the risk of getting the flu by getting vaccinated and practicing good hygiene, such as washing your hands frequently, covering your mouth and nose when you cough or sneeze, and avoiding close contact with sick individuals.

The flu vaccine is typically available in the fall, and it is recommended that people get vaccinated before the start of the flu season. The vaccine is usually effective in reducing the severity and duration of the flu if you do get infected.