On May 11, 2001, the Food and Drug Administration (FDA) licensed a combined hepatitis A and B vaccine (Twinrix^®) for use in persons aged >18 years. Twinrix was manufactured and distributed by GlaxoSmithKline Biologicals (Rixensart, Belgium), and is made of the antigenic components used in Havrix and Engerix-B (GlaxoSmithKline). The antigenic components in Twinrix had been used routinely in separate single antigen vaccines in the United States since 1995 and 1989 as hepatitis A and B vaccines, respectively.

Each dose of Twinrix contains at least 720 enzyme-linked immunosorbent assays units of inactivated hepatitis A virus and 20 mcg of recombinant hepatitis B surface antigen (HBsAg) protein, with 0.45 mg of aluminum in the form of aluminum hydroxide and aluminum phosphate as adjuvants, 5.0 mg 2-phenoxyethanol as a preservative, and pH stabilizer in normal saline. Trace amounts of thimerosal (<1 µg mercury), neomycin (<20 ng), formalin (<0.1 mg), and yeast protein (<5%) also are present from the manufacturing process.

Twinrix is indicated for vaccination of persons aged >18 years against hepatitis A and B. Any person in this age group having an indication for both hepatitis A and B vaccination can be administered Twinrix, including patients with chronic liver disease, users of illicit injectable drugs, men who have sex with men, and persons with clotting factor disorders who receive therapeutic blood products. For international travel, hepatitis A vaccine is recommended for travelers to areas of high or intermediate hepatitis A endemicity; hepatitis B vaccine is recommended for travelers to areas of high or intermediate hepatitis B endemicity who plan to stay for >6 months and have frequent close contact with the local population. Primary vaccination consists of three doses, given on a 0-, 1-, and 6-month schedule, the same schedule as that used for single antigen hepatitis B vaccine.