However, there's a strong incentive for this vaccine to succeed.
A vaccine against HIV has been a real challenge for scientists, because of this virus many strains. Should it prove effective, doctors could administer vaccine on a broad scale where past vaccines would have only worked for small populations even if they'd worked well.
"The challenges in the development of an HIV vaccine are unprecedented, and the ability to induce HIV-specific immune responses does not necessarily indicate that a vaccine will protect humans from HIV infection".
"However, it's important to be cautious and be clear that there's a lot of work to do before an effective HIV vaccine is readily available".
They found that "all vaccine regimens tested were capable of generating anti-HIV immune responses in healthy individuals", meaning that the study participants built up some kind of protection from the virus.
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A vaccine is a vital weapon in the war against the virus, which infects an 1.8 million people each year.
Preliminary results of the APPROACH trial in humans were presented at last year's International AIDS Conference; now they appear in peer-reviewed form for both the human and non-human studies in The Lancet. Over the course of the 48-week trial, each participant received 4 vaccinations, all of which "produced an anti-HIV immune system response and were found to be safe".
The study used so-called "mosaic" vaccine combinations.
Dan H. Barouch, MD, PhD, is Director of the Center for Virology and Vaccine Research at Beth Israel Deaconess Medical Center. To address these methodological issues, Barouch and colleagues evaluated the leading mosaic adenovirus serotype 26 (Ad26)-based HIV-1 vaccine candidates in parallel clinical and pre-clinical studies to identify the optimal HIV vaccine regimen to advance into clinical efficacy trials.
He adds: "These results should be interpreted cautiously". Buchbinder explained that Imbokodo is from a South African proverb about the strength of women that says "you strike the women, you strike the rock", as the trial is in the process of enrolling 2,600 non-pregnant HIV-negative women ages 18 to 35.
An experimental HIV vaccine showed promise of protecting healthy adults from contracting the deadly virus that killed millions of people in the past years.
"The road to the clinic is still unpredictable since the exact mode of action in humans is still unknown and the 67 percent protection in monkeys might not be replicable in humans", said George Williams Mbogo from the Burnet Institute in Australia, who wasn't involved in the study.