On Mar. 28, 2007, the U.S. Food and Drug Administration (FDA) announced that GlaxoSmithKline (King of Prussia, Pennsylvania) received approval for an alternate schedule for Twinrix, a combined hepatitis A and hepatitis B vaccine.

Twinrix was first licensed by FDA in 2001 on a 3-dose schedule (0, 1, and 6 months) for vaccination of persons aged >18 years. Using the newly licensed, alternate 4-dose schedule, Twinrix doses can be administered at 0, 7, and 21–30 days, followed by a dose at 12 months.

In immunogenicity studies among adults aged >18 years, the first 3 doses of the alternate schedule provided equivalent protection to the first 2 doses in the standard 3-dose Twinrix series. The first 3 doses of the alternate schedule also have proven effective in providing protection equivalent to a single dose of monovalent hepatitis A vaccine and to 2 doses of monovalent hepatitis B vaccine, administered using the licensed schedules for the monvalent vaccines. Thus, the alternate 4-dose schedule can be useful if vaccination with Twinrix has been initiated and travel or other potential exposure is anticipated before the second dose of Twinrix (or monovalent hepatitis B vaccine) is due, according to the standard 3-dose schedule (i.e., 1 month after the first dose).