A new clinical trial has produced a combination of two genetically engineered vaccines- neither of which had worked before in humans- that was declared a qualified success after six years of testing on more than 16,000 volunteers in Thailand. Those who were vaccinated became infected at a rate nearly one-third lower than the others.
The trial used a combination of ALVAC HIV - from Sanofi-Aventis, the French pharmaceutical company - as "prime" vaccine, with a second vaccine booster called AIDSVAX B/E, developed by GenVax of the US, and since ceded to the non-profit group Global Solutions for Infectious Diseases. It was overseen by the Thai authorities, with US military support. The work, beginning in 2003, was complex, involving initial interviews of 60,000 people aged 18-30 from the Rayong and Chon Buri provinces, before 16,402 initially took part. Almost 0.8 per cent contracted HIV, including 51 per cent who were vaccinated and 74 per cent who were not.
But the findings leave many questions unanswered: most importantly, while those who were vaccinated had a lower rate of HIV infections, it had no effect in reducing the "viral load" or presence of HIV for those who had been vaccinated. This reinforces uncertainty over the mechanism by which vaccines affect the human immune system. There are also uncertainties about the longer term probability of infection and the development of HIV in those who have been vaccinated, and the effects in other groups at higher risk of HIV including sex workers, gay men and intravenous drug users.
"We don't really know why and how this vaccine worked and did what it did," said Dr. Alan Bernstein, executive director of the Global HIV Vaccine Enterprise, an alliance of AIDS scientists, governments and donors.
"This trial is raising more questions almost than it's answering," he said. "It's opened the door and it's opened up a whole lot of questions that are answerable and will be answered over the next months and years to come."
Because of the long time frame, health advocates warn that people should not count on a potential vaccine to treat and contain infections.
An estimated 33.2 million people around the world were living with HIV in 2007, according to the Joint United Nations Program on HIV/AIDS. The Centers for Disease Control and Prevention estimates that about 1.1 million adults and adolescents were living with diagnosed or undiagnosed HIV infection in the United States at the end of 2006.