Flu shots are not allowed for colds and are recommended after recovery. If you are in the course of a cold, you should not receive the flu vaccine. On the one hand, this is because the immune system is relatively weak at this time, and the vaccination is needed to stimulate the immune system to produce antibodies against the influenza virus to achieve the purpose of prevention. When the immune system is weak, it is unable to produce enough antibodies, or the titer of antibodies is insufficient to achieve the preventive effect. On the other hand, adverse reactions may occur after vaccination, such as headache, cough and fatigue. Such symptoms can occur during a cold, and if the vaccine is administered at this time, it is impossible to distinguish between an adverse reaction to the vaccine and the cold itself. It is recommended that the vaccine be administered after full recovery, subject to the advice of the staff at the vaccination site.