ATN 052 was a laboratory-based study that was designed to study how individuals differ in their immune responses to the hepatitis B vaccines. These vaccines make specific proteins called antibodies that protect people against hepatitis B virus (HBV) infection if they come into contact with the virus. The benefits of safe and effective vaccination can be less than expected because some individuals do not produce enough of these antibodies. Different forms of human genes and other factors like age and gender may account for occasional failure in vaccination. The goal of ATN 052 was to test if genetic differences are indeed related to antibody response to hepatitis B vaccine.