In April 2007, the U.S. Food and Drug Administration (FDA) approved an alternative schedule for the combined hepatitis A and hepatitis B vaccine Twinrix (GlaxoSmithKline). The vaccine was first licensed in 2001 for vaccination of persons 18 years and older with a schedule of three doses administered at zero, one, and six months. An alternative four-dose schedule can now be used, with doses administered at zero, seven, and 21 to 30 days, and at 12 months.

Studies showed that the first three doses of the four-dose schedule provide equivalent protection to the first two doses in the three-dose series, as well as to a single dose of monovalent hepatitis A vaccine and to two doses of monovalent hepatitis B vaccine. The FDA suggests that the four-dose schedule may be useful if vaccination with the combination vaccine has been initiated but potential exposure (e.g., through travel) is expected before the second dose is due, according to the standard three-dose schedule. Additional information is available from the manufacturer's package insert and GlaxoSmithKline Vaccines (telephone, 800-366-8900).