It is usually possible to produce antibodies to the influenza virus after recovering from the flu, which allows the body to reduce the probability of secondary infections in a short period of time. Recovery from influenza means that the symptoms of influenza have completely disappeared and the influenza virus has been completely eliminated from the body. Similar to other viral infections, the entry of influenza virus into the organism is equivalent to the entry of antigenic substances into the body, which stimulate the body’s third defense system, i.e., the humoral immune system and the cellular immune system. The antigen can stimulate the humoral and cellular immune response, prompting the body to produce influenza virus-related antibodies, which can not only neutralize the influenza virus in the body, but also have residual antibodies present in the body after the influenza virus is completely eliminated, so that when the body is re-exposed to the virus, it can immediately trigger the secondary immunity and neutralize the virus, thus reducing the rate of secondary infections within a short period of time.