Hepatitis A, also known clinically as viral hepatitis A, is an infectious disease caused by the hepatitis A virus, which is a predominantly inflammatory disease of the liver. Generally, people of all ages can contract the disease, but children and adolescents are the main targets. Therefore, it is important for today’s young children to be vaccinated against hepatitis A in a timely manner so that they can prevent the disease. How long is the hepatitis A vaccine valid? The expiration date of the hepatitis A vaccination Currently, there are two types of hepatitis A vaccines: inactivated vaccine and live attenuated vaccine (live vaccine includes water injection and lyophilized). Inactivated vaccines are composed of purified whole virus particles after inactivation, while live attenuated vaccines are composed mainly of attenuated live virus. Live attenuated vaccine water injection has the feature of low price, and hepatitis A vaccine can be valid for more than 5 years, but it has the weakness of poor vaccine stability. The lyophilized live attenuated vaccine that overcomes this weakness has been introduced in recent years. Inactivated vaccines have high antibody titers, and the validity of hepatitis A vaccine can last for more than 20 years. Since the virus is fully inactivated, there is no risk of virulence recovery, and safety is fully guaranteed, so inactivated vaccines are used abroad. The best time to receive hepatitis A vaccine The inactivated hepatitis A vaccine is one of the vaccines recommended by the World Health Organization, and children aged 1 year old have a weak resistance to the virus, so it is best to receive the hepatitis A vaccine. A high level of antibodies can be produced about 8 weeks after the hepatitis A vaccination and good immunity can be obtained. Therefore, hepatitis A vaccine has good immune protection. The specific timing of hepatitis A vaccination is as follows: 1) Initial vaccination: for hepatitis A susceptible people over 1 week old; 2) Boosted immunization 6 months after the initial vaccination; 3) Boosted immunization for people who have received live hepatitis A vaccine in the past, regardless of the length of the interval. In recent years, the observation of population vaccination proves that if the live attenuated hepatitis A vaccine is immunized by the “two-dose method”, the anti-HAV positivity rate can reach 100% and the anti-HAV titer can reach more than 1000mIU/ml at an interval of 1 month, 3 months, 6 months or 12 months. Live attenuated hepatitis A vaccine is recommended to be administered twice for lifelong immunity.