The second dose of influenza vaccine is recommended to be given 1 month apart and no later than 3 months. Influenza vaccination can be effective in preventing influenza in babies with weak resistance. For infants and toddlers between 6 months of age and 3 years of age, two doses are required for the initial vaccination. Since the number of antibodies produced by the first dose may be insufficient, a second booster dose is required after an interval of 1 month. However, the interval should not exceed 3 months at the latest, because more than 3 months may affect the production of antibodies, and the longer the interval, the greater the impact. In addition, the flu vaccine is mostly effective for 1 year after vaccination, and a new vaccination is required the following year. For children and adults over 3 years old, a vaccination within 1 year is sufficient, and it is recommended that the vaccination be given between September and November each year. After receiving the flu vaccine, you must stay in the hospital for 30 minutes to observe and leave without any abnormalities. In addition, influenza vaccination will reduce the risk of influenza, but it does not mean that you will not be infected at all, so you still need to be protected during the influenza epidemic.