Hepatitis A vaccine is a vaccine used to prevent hepatitis A. It is now one of the main vaccines given to children in China and was included as one of the expanded immunization vaccines in May 2008, with some provinces and cities already offering free hepatitis A vaccination. Inactivated hepatitis A vaccine is one of the vaccines recommended by the World Health Organization. Children aged 1 year old are less resistant to the virus and are best vaccinated against hepatitis A. A very high level of antibodies can be produced about 8 weeks after hepatitis A vaccination and good immunity is obtained. Therefore, hepatitis A vaccine has good immune protection. The two main types of hepatitis A vaccines available in the market are inactivated hepatitis A vaccine and live attenuated vaccine. Due to the different preparation principles, there are differences in effectiveness and safety. Compared to live attenuated vaccines, inactivated vaccines have better stability. Both inactivated and attenuated vaccines are used to achieve immunity by invading the body and causing an immune response, thus causing the body to develop immune memory. The specific timing of hepatitis A vaccination is as follows: 1. Initial vaccination time: for hepatitis A susceptible people over one year old; 2. Six months after the initial vaccination, booster immunization is available; 3. Those who have received live hepatitis A vaccine in the past can receive booster immunization regardless of the interval. Effective period: In recent years, it has been observed that if the live attenuated hepatitis A vaccine is immunized by the “two-dose method” with an interval of 1 month, 3 months, 6 months or 12 months, the anti-HAV positivity rate can reach 100% and the anti-HAV titer can reach more than 1000 mIU/ml. Live attenuated hepatitis A vaccine is recommended twice for lifelong immunity. Many mothers question the safety of hepatitis A vaccine, that is, they are worried about the side effects of the vaccine. In fact, the safety of a vaccine should be evaluated in comparison to its preventive effect on the disease. When a mother weighs the side effects of the vaccine against the threat of the disease, the vaccine is actually a safe choice for her baby to prevent the disease. The hepatitis A vaccine produces very high levels of antibodies and good immunity in about 8 weeks after vaccination. Therefore, hepatitis A vaccine provides good immune protection. Compared to inactivated vaccines, weak vaccines produce faster and stronger immunity, but for people who are weak or have their own diseases, it is recommended to strengthen their health or recover from diseases before vaccination, and not to take antiviral drugs while vaccination is in progress, and they need to strengthen their nutritional intake. All children and adults who are susceptible to the hepatitis A virus and who are at least 1 year old should be vaccinated. The vaccination stimulates the body to develop immunity against the hepatitis A virus and is used to prevent hepatitis A. Inactivated hepatitis A vaccine is suitable for children, medical workers, food industry workers, and people with occupational exposure to the hepatitis A virus, and the initial vaccination for children is at least one year old, while there is no age limit for adults. Vaccination should be delayed in cases of fever, acute illness, and progressive chronic illness. A booster immunization can be given 3 years after vaccination.