Two doses of the vaccine are usually considered necessary for children between the ages of 6 months and 3 years, and one dose is usually sufficient for children over the age of 3 years and adults. The influenza vaccine is a vaccine used to prevent the influenza virus from attacking the body. The population is generally susceptible to the influenza virus, and the influenza vaccine is indicated for susceptible people over the age of 6 months. Because the subtypes of influenza viruses that are prevalent during a pandemic vary from year to year, vaccination is usually required annually. Infants and young children aged 6 months to 3 years are more susceptible to influenza viruses than children and adults aged 3 years or older, so it is recommended that they receive two doses of the vaccine, and children and adults aged 3 years or older can achieve better preventive health effects with one dose.