Influenza A, i.e. Influenza A H1N1, complications include damage to the respiratory system, nervous system, cardiovascular system and so on. 1. Respiratory system: the most common complication of influenza A is viral pneumonia, which can also be followed by acute respiratory distress syndrome, pulmonary hemorrhage, pleural effusion, respiratory failure and other complications. 2. Neurological system: drowsiness, mental changes, meningitis, acute necrotizing encephalopathy, shock and other complications can occur. 3. Cardiovascular system: complications such as myocarditis, pericarditis and cardiac insufficiency can occur. 4. Other: Influenza A can also present complications such as sudden high fever, pancytopenia, renal failure, sepsis, shock and Reye’s syndrome. The patient’s pre-existing underlying disease can also be aggravated. It is recommended that patients consult a doctor when complications occur and take appropriate measures for treatment.