The hepatitis A vaccine is mainly used to prevent hepatitis A. There are two types of hepatitis A vaccines on the market today, one is a lyophilized live attenuated hepatitis A vaccine and the other is an inactivated hepatitis A vaccine. The hepatitis A vaccine has good immune protection, and after receiving the hepatitis A vaccine, a high level of antibodies can be produced in about 4-8 weeks, giving the body a good immune system. Currently, hepatitis A has been included as one of the main vaccines in the childhood immunization program, and children and adults over the age of one year are generally susceptible to hepatitis A virus. Therefore, hepatitis A vaccination is usually given when the child is about 18 months old, and the vaccination should be given when the child is healthy, not when the child has a disease.