HBvaxPRO vaccine in a glass vial. This vaccine contains an inactivated extract of the hepatitis B virus, which infects the liver. When injected, the vaccine stimulates the body's immune system to produce antibodies, but without causing an infection. The immune system can then respond quickly against future infections by the hepatitis B virus. The HBvaxPRO vaccine is only given to people at risk, such as health workers and drug addicts. The vaccine is given in at least three doses and it can take up to six months for adequate numbers of antibodies to be formed to provide immunity.