Influenza virus is an easily mutated virus that is not very resistant to the outside world and can easily cause pandemics. The main source of infection is the patient, and then the hidden infected person, and infected animals can also be the source of infection. Influenza virus is mainly spread by droplets with influenza virus, entering the human body through the respiratory tract, a few can also be infected by sharing handkerchiefs, towels and other indirect contact. When the virus enters the population, it is highly contagious and can spread rapidly. The speed and breadth of transmission are related to the population density, and the population is generally susceptible. The incubation period depends mainly on the amount of invasive virus and the immune status of the body, and is usually 1-4 days.