Twinrix is a vaccine against hepatitis A and hepatitis B, manufactured by GlaxoSmithKline. Twinrix is administered over three doses. The name was created because it is a mixture of two earlier vaccines — Havrix, an inactivated-virus Hepatitis A vaccine, and Engerix-B, a recombinant Hepatitis B vaccine. Twinrix, Havrix and Engerix-B are registered trademarks of GlaxoSmithKline; if the same vaccine is available from others, it will have another name. Twinrix first entered the market in early 1997.