If you have had influenza A once, you may still get it a second time. Influenza A is an acute infectious disease caused by influenza A virus infection, mainly through droplet transmission and close contact transmission, causing high fever, myalgia, malaise, loss of appetite, runny nose, nasal congestion, children are prone to abdominal pain, vomiting, diarrhea and other symptoms. Influenza A is mainly treated with supportive therapy, and antiviral therapy with oseltamivir is needed for the elderly, children, patients with underlying diseases, and those with severe illnesses. Influenza A virus is the most mutable of the influenza viruses. The surface antigen of the virus often undergoes subtle mutations to produce new strains of the virus, which can evade the recognition of the human immune system of previous influenza infections; in addition, the influenza A virus also undergoes mutations to produce new subtypes, to which the human body has little or no resistance. Therefore, even if you have had influenza A once, it is difficult to avoid being infected again. Prevention is the mainstay of influenza A. It is recommended to get vaccinated against influenza every year, reduce the number of people going to places where people gather, wash hands frequently and wear masks for prevention.