An AIDS vaccine developed by GlaxoSmithKline has been shown to stave off the disease in monkeys for over a year. Human Phase I clinical tests are expected to start later this year. If the product proves successful in human testing, Glaxo may combine the vaccine with a cocktail of its existing AIDS drugs. Merck, VaxGen, Aventis, and Chiron are among the other companies that have tested or are testing HIV vaccines.