The encephalitis B vaccine prevents epidemic encephalitis B. The first dose is given at 8 months of age, and another dose is given at 2 years of age for booster immunization. Encephalitis B is an acute infectious disease caused by the encephalitis B virus, which is transmitted through mosquito bites and mainly affects the human central nervous system. The main manifestations of BSE include high fever, headache, vomiting, loss of appetite, increased intracranial pressure, mental disorders, mental retardation, impaired consciousness or confusion, and in severe cases, coma or even death. After receiving the BSE vaccine, the body can produce enough immunity to fight against the virus and avoid the disease once it is infected with the BSE virus. Adverse reactions to B encephalitis vaccination are rare, mainly manifested as transient fever or redness, swelling and pain at the vaccination site, which usually do not require special treatment and usually heal themselves in 1-2 days. If fever persists, it is recommended to visit a hospital for consultation and treatment.