Combined hepatitis A and B vaccine, is used to provide protection against hepatitis A and hepatitis B.^[3][7] It is given by injection into muscle.^[8]

It is used in areas where hepatitis A and B are endemic, for travelers, people with hepatitis C or chronic liver disease, and those at high risk of sexually transmitted diseases.^[7]

The combined vaccine is as safe and protective as if given as separate hepatitis A and B vaccines.^[7] It is generally well-tolerated.^[9] Common side effects are mild and include redness and pain at the injection site, where a small lump may appear.^[8] Feeling faint or tired, or a headache may occur.^[8] Other side effects include numbness, tingling, rash, bruising, abnormal bleeding such as from the nose or gums, weak muscle or pain.^[8] Severe side effects are rare and include an allergic reaction and seizures.^[8]

It is widely available.^[7]

Routine Twinrix vaccination is administered by intramuscular injection in the deltoid area using a schedule of three separate doses at 0, 1, and 6 months ([minimum intervals: 4 weeks between doses 1 and 2, 5 months between doses 2 and 3]).^[3][10] In some circumstances, an accelerated dosing schedule of 0, 7 and 21 to 30 days followed by a booster at 12 months can be used and was shown to have similar efficacy as the traditional schedule.^[11]

The U.S. Centers for Disease Control and Prevention (CDC) reports that clinical trials found the following levels of protection against Hepatitis A and Hepatitis B one month after each dose:^[12]

A: 93.8%, 98.8%, 99.9%

B: 30.8%, 78.2%, 98.5%

Twinrix is a brand manufactured by GlaxoSmithKline Biologicals. The full generic name is hepatitis A inactivated & hepatitis B (recombinant) vaccine.^[13] 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.^{[citation needed]} Twinrix first entered the market in early 1997.^[14]

In the United States, Twinrix is approved by the Food and Drug Administration (FDA) for those aged 18 and older.^[3][12] In some countries outside the United States, notably Canada and in the European Union, Twinrix is known as Twinrix Adult or Ambirix and a pediatric formulation, called Twinrix Junior or Twinrix Paediatric, is available.^{[15][16][17][18][19][20][21][22][excessive citations]}