Patients with influenza A usually have a high fever for 3-5 days, but this varies from person to person and cannot be generalized. When the virus invades the body, it activates the immune system and raises the body temperature, which usually lasts for 3-5 days. High fever will lead to water loss in the body, so pay attention to hydration. You can take physical cooling methods at home, such as using medical alcohol or warm water to wipe the whole body, placing cooling ice packs in the armpits, forehead and other parts. In severe cases, medication should be used to lower the temperature under the guidance of a doctor.