Influenza can be fatal. Influenza, short for influenza, is an acute respiratory infection caused by the influenza virus when it invades the body. It usually starts rapidly with high fever, headache, conjunctivitis, and generalized muscle aches and pains and other obvious symptoms of toxicity. Influenza viruses are highly mutable and the population is generally susceptible to them. The outcome of influenza virus treatment is related to the virulence of the virus, autoimmune status and other factors. Influenza A viruses, etc. often cause pandemics and severe illness, while influenza B and C viruses, etc. can cause epidemics or epidemics and relatively mild illness. Weakened individuals (e.g., the elderly, those with comorbidities, etc.) are more likely to develop pneumonic influenza, which may be life-threatening if the disease continues to progress.