The flu (influenza) is a highly infectious disease caused by influenza viruses.
A virus is a microorganism. A microorganism is so tiny that you need a powerful microscope to see it.
There are three types of flu virus: A, B and C. Influenza A and B viruses cause almost all of the illness. The symptoms of influenza C infection are usually weak. Flu occurs every year mainly during the winter months.
sneezes. It can also be spread when you touch another infected person's respiratory droplets and then touch your own face or eyes.

The influenza virus attacks the respiratory tract (your ears, nose, and throat). The infection causes fever, chills, cough, body aches, headaches, and sometimes earaches or sinus problems.
Although most people recover from flu within a week, for some people the infection is more serious and leads to problems. These illnesses are dangerous especially for babies and kids under age 5, people older than 50, and adults and kids who have health problems, such as diabetes and asthma.Since flu activity is increasing, health experts recommend a yearly flu vaccine as the first and most important step in protecting against this serious disease.