Influenza is an acute respiratory disease caused by influenza viruses. There are three types of the virus including A, B and C. Both type A and type B viruses can cause acute febrile respiratory tract infection, characterized by sudden fever, headache, muscle pain, cough, sore throat, nasal congestion and general malaise. The main transmission of influenza is through those highly contagious aerosol droplets containing influenza virus passed from infected people to susceptible population. Each year in the fall and winter infection of influenza is widespread in various age groups, with high incidence rate. Although influenza is generally a self-limiting disease, but in children, the elderly (especially those above 65 years old and those with chronic heart, lung, kidney, liver, blood or metabolic diseases such as diabetes or other certain diseases) and those with poor immunity function, influenza can easily lead to serious flu complications such as pneumonia, resulting in severe increase of morbidity and mortality.