Twinrix is an inactivated combination vaccine containing both hepatitis A virus (HAV) and HBV antigens. The vaccine contains 720 EL.U. of hepatitis A antigen (half of the Havrix adult dose) and 20µg of hepatitis B antigen (the full Engerix-B adult dose). In the U.S., Twinrix is licensed for use in people who are age 18 years or older. It can be administered to people who are at risk for both hepatitis A and hepatitis B, such as certain international travelers, people with chronic liver disease, men who have sex with men, illegal drug users, or to people who simply want to be immune to both diseases. A Twinrix series consists of 3 doses given intramuscularly on a 0, 1, and 6 month schedule.