JOHANNESBURG, 24 September 2009 (PlusNews) - A six-year clinical
trial in Thailand has yielded the first ever evidence that an
AIDS vaccine can provide some protection against HIV infection.
The trial team in Bangkok, Thailand's capital announced on 24
September that rates of HIV infection were 31 percent lower in
trial participants who got the vaccine than in those who received
"These new findings represent an important step forward in HIV
vaccine research," said Dr Anthony Fauci, director of the US
National Institute of Allergy and Infectious Diseases (NIAID),
the main funder of the trial.
The study, known as RV144, began enrolling 16,000 HIV-negative
men and women between the ages of 18 and 30 in October 2003. Half
the volunteers received a placebo; the other half were given
shots containing two different vaccines. The first, called
ALVAC-HIV, used a disabled form of a bird virus known as canary
pox to deliver synthetic versions of three HIV genes into the
body. The second, called AIDSVAX, was composed of a genetically
engineered version of an HIV protein.
The synthetic HIV components in both vaccines were based on
subtypes B and E of the virus, which are most common in Thailand,
the US and Europe. Scientists do not yet know whether the vaccine
would be effective against other strains, such as subtype C,
which is most prevalent in sub-Saharan Africa.
The trial was designed to evaluate whether the combined vaccines
lowered HIV infection risk, and whether they had any impact on
viral load [the amount of HIV circulating in the bloodstream] in
the volunteers who became infected.
Of 8,197 people given the vaccine regimen, 51 became infected,
compared to 74 of the 8,198 volunteers who received the placebo.
This result is considered "statistically significant", meaning
that the difference is unlikely to be a coincidence. The vaccine
did not have any effect on viral load.
"Today's result is not the beginning of the end of the epidemic,
it's the end of the beginning of finding an AIDS vaccine. It's a
thrilling moment," Mitchell Warren, executive director of the
AIDS Vaccine Advocacy Coalition (AVAC), told IRIN/PlusNews on the
phone from New York. However, he emphasized that additional
studies and analysis were needed to confirm and understand the
The vaccine's modest effectiveness means it is unlikely to be
licensed or produced in large quantities in Thailand, where the
rate of HIV infection is relatively low. However, Prof Gavin
Churchyard, CEO of the Aurum Institute, a non-profit medical
research organization based in South Africa, said even an AIDS
vaccine that was only 30 percent effective could have an impact
in southern Africa, where HIV infection rates are much higher,
"but we would need to know if it would work in this population".
Churchyard said the results had come as a surprise to many in the
vaccine field. "We weren't actually expecting a positive result,"
he commented. Previous efficacy trials of AIDSVAX, the second
vaccine in the regimen, had found no benefit and the decision to
go ahead with the large-scale trial in Thailand had generated
Warren noted that vaccine science had evolved considerably since
the trial was launched in 2003. "There are new ideas and
approaches that no one imagined six years ago. Anytime you start
a trial, it's like buying a new computer - it's outdated before
you even get it out of the box." He added that whether or not the
approach used in the trial was determined to be the most
effective, the findings would still influence future strategies.
Good news at last
The positive results from the Thai trial are expected to give a
crucial boost to a field in desperate need of good news after a
series of setbacks in recent years. A four-continent trial of a
vaccine developed by pharmaceutical company Merck was halted in
2007 after preliminary results suggested that it not only did not
provide protection against HIV, but might actually increase the
risk of infection.
Dr Glenda Gray of the Perinatal HIV Research Unit (PHRU) at the
University of the Witwatersrand in Johannesburg, chief
investigator in the South African arm of the Merck vaccine trial,
told IRIN/PlusNews the outcome in Thailand was "a huge step
forward - it opens up the field again and gives us an indication
that this [a vaccine] is possible."
The results are also significant for the future of two HIV
vaccines that began small-scale human trials in South Africa in
July. One of the vaccines uses components from the family of pox
viruses similar to those used in one of the Thai vaccines. "It
means, hopefully, there'll be more interest in our vaccine," said
Gray, the lead investigator of the trials being conducted by the
South African AIDS Vaccine Initiative (SAAVI) and NIAID.
"We are planning a larger trial next year and having these
results makes it much easier for us to convince funders to go
ahead with the next phase," Gray said.
More information on the Thai trial results will be presented at
an AIDS vaccine meeting in Paris in October.