The hepatitis B vaccine requires three doses because after the first dose, only 30% of people usually develop hepatitis B surface antibodies, and the antibodies are unstable. After the second dose, 90% of people will develop hepatitis B surface antibodies, and after the third dose, 96% of people will develop hepatitis B surface antibodies, and the antibodies are more stable and will continue to be high. The hepatitis B vaccine stimulates the body to produce hepatitis B antibodies, which neutralize and clear the hepatitis B virus in the body. When the body is exposed to the hepatitis B virus, the specific antibodies produced after successful hepatitis B vaccination prevent the hepatitis B virus from infecting the body, thus providing immunity to hepatitis B virus infection.