The hepatitis B vaccine can protect a person against hepatitis B for at least 23 years. People who should get the hepatitis B vaccine include healthcare workers, international travelers, and people with a chronic liver disease, among others. There are also some people who should not get the vaccine, including those who have had a severe (life-threatening) allergic reaction to a previous dose of hepatitis B vaccine and those who have had a severe allergic reaction to any vaccine component or to baker's yeast (the kind used to make bread). Before receiving the hepatitis B vaccine, you should let your healthcare provider know if you have any severe allergies. The hepatitis B vaccine is given as a series of injections -- a single shot, followed by a second injection one month later, and then a third shot six months later.