Scientists at Merck and Co.'s vaccine research headquarters in suburban Philadelphia are testing two experimental HIV vaccines in early human trials. In earlier laboratory tests, the vaccines did not prevent monkeys from contracting a simian version of HIV but did control the virus in the animals so that the monkeys never developed AIDS. The company is now conducting 10 Phase I human studies involving 1,300 volunteers around the country. The studies will explore the vaccine's safety and record any immune response. Later tests will determine whether the vaccine prevents people from developing AIDS. Results from the Phase I trials are expected next year. If test results are promising, studies on the vaccine's effectiveness in humans could take another few years, until 2008 or 2009.
Merck's lead vaccine uses a common-cold adenovirus to carry genetic material from HIV into the body in order to produce an immune response. In Merck's monkey studies, a "naked DNA" inoculation with an adenovirus booster produced the best immune response.