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.