General Information

Twinrix is a combination hepatitis vaccine.

Twinrix is indicated for active immunization against disease caused by hepatitis A virus and infection by all known subtypes of hepatitis B virus in patients 18 years of age and older.

Twinrix is administered by intramuscular injection.

• Standard Dosing: A series of 3 doses (1 mL each) given on a 0-, 1-, and 6-month schedule.
• Accelerated Dosing: A series of 4 doses (1-mL each) given on Days 0, 7, and 21 to 30 followed by a booster dose at Month 12

Mechanism of Action

Hepatitis A

The course of infection with hepatitis A virus (HAV) is extremely variable, ranging from asymptomatic infection to fulminant hepatitis.3 The presence of antibodies to HAV (anti-HAV) confers protection against hepatitis A disease. However, the lowest titer needed to confer protection has not been determined. Natural infection provides lifelong immunity even when antibodies to hepatitis A are undetectable. Seroconversion is defined as antibody titers equal to or greater than the assay cut-off (cut-off values vary depending on the assay used) in those previously seronegative.

Hepatitis B

Infection with hepatitis B virus (HBV) can have serious consequences including acute massive hepatic necrosis and chronic active hepatitis. Chronically infected persons are at increased risk for cirrhosis and hepatocellular carcinoma. Antibody concentrations ≥10 mIU/mL against HBsAg are recognized as conferring protection against hepatitis B virus infection.

Side Effects

Adverse effects associated with the administration of Twinrix may include, but are not limited to, the following:

• injection site soreness
• redness
• headache
• fatigue

Clinical Trial Results

Data was analyzed from 1,551 subjects in 11 trials following administration of three doses of Twinrix on a 0-, 1- and 6-month schedule. In these trials, 99.9% of the subjects showed a response against the hepatitis A component of Twinrix and 98.5% demonstrated a response against the hepatitis B component.

One of the 11 trials was a randomized, multicenter comparative trial conducted in the United States. In this trial, an immunogenicity analysis was performed in 533 subjects who completed the study according to protocol. Subjects received either Twinrix on a 0-, 1-, 6-month schedule or Havrix (Hepatitis A Vaccine, Inactivated) on a 0-, 6-month schedule and Engerix-B [Hepatitis B Vaccine (Recombinant)] on a 0-, 1-, 6-month schedule, given concurrently in opposite arms.

Results from the trial demonstrated that subjects receiving three doses of Twinrix had antibody responses similar to those of subjects receiving monovalent hepatitis A and B vaccines separately over the same time period. The antibody responses to the hepatitis A and B components in the Twinrix group were 99.6 and 95.1%, respectively, and 99.3 and 92.2% in the Havrix and Engerix-B group.