Drugmakers Merck and Aventis have begun human clinical trials of a novel combination HIV vaccine. The trials are hoped to assess whether the addition of a vaccine made by Aventis to Merck's vaccine candidate will prove more effective than either alone. Merck began human testing of its HIV vaccine in late 1999. Merck's current candidate, known as the replication-defective adenovirus type 5 vector, is based on a modified common-cold virus that is used to deliver an HIV gene into cells to produce an immune response to HIV. Aventis's Alvac HIV vaccine has been in development since 1992 and is a canarypox vector, which delivers HIV genes into cells.
Earlier this year an experimental HIV vaccine by Vaxgen was shown to reduce the HIV infection rate by just 3.8% in 5,400 men and women considered at high risk. At least 30 other HIV vaccines are in various stages of development.