Two candidate vaccines have been identified, both of which trigger a strong immune system response over several months to more than one strain of the virus, with minimal side effects in healthy volunteers. The level of antibodies produced is similar to that seen in people infected with the live HIV virus.
The vaccines have progressed to phase two trials - the only two vaccines to have done so - in healthy high-risk volunteers. Plans to recruit thousands more healthy volunteers in the US for the third and final phase of trials are under way for 1994 and 1995.
Dr Dani Bolognesi, director of the Central Immunology Laboratory at Duke University, North Carolina, told the international Aids conference in Berlin: 'HIV vaccine development can be considered at a crossroads, and is in a position to turn a corner'. Another 20 candidate vaccines are in preliminary trials worldwide.
Reports of promising vaccines are a feature of every Aids conference, but Dr Bolognesi gave the most positive report to date.
The two vaccines, known as rgp 120MN and rgp 120 SF-2, trick the body into thinking HIV has infected it. To imitate HIV, scientists used genetic engineering techniques to recreate the outer coat of the virus. The immune system should respond by producing cells which target and destroy HIV. Refinements in the genetic engineering technique used to produce parts of the viral coat mean they now mimic the live virus much more closely than early attempts.
Three doses of rgp 120MN vaccine given over six months stimulated antibodies to three strains of the virus. Three doses of the second vaccine also produced high levels of antibodies to three different strains.