The frustrating quest to develop a vaginal gel to prevent HIV
infection was dealt a fresh blow on Monday as researchers announced
that the first prototype to complete advanced clinical trials was
Carraguard, a candidate microbicide produced by the Population
Council that had spent three years in large-scale "Phase 3" trials, was
unable to prevent transmission of the Aids virus, the investigators
But the gel was found to be safe for long-term vaginal use, a
finding they described as extremely promising.
"This is the first phase 3 microbicide efficacy trial to be
completed with no safety concerns," said principal investigator
Khatija Ahmed. "(...) However, the study was unable to show
Carraguard's efficacy in preventing male-to-female transmission of
The trial ran from March 2004 to March 2007 at three sites in South
Africa among 6,262 women.
Half of the volunteers were given the Carraguard gel and condoms,
while the other half were given a placebo gel and condoms. All were
given HIV education and safer-sex counselling.
In the Carraguard group, 134 new HIV infections occurred, slightly
fewer than the 151 in the placebo group. But Ahmed said the difference
was not statistically significant and did not constitute evidence that
Carraguard was effective.
It is the third major setback in the seven-year-long drive to
develop a vaginal microbicide, the term for a cream that would block or
kill the Aids virus during vaginal intercourse.
Microbicides are one of the most eagerly-sought avenues in the war
on Aids, where at present there is neither a cure nor a vaccine and
prevention depends on the condom or abstinence.
Scientists are grappling for a means by which women, who are
physically more at risk from Aids infection than men, can protect
themselves without having to rely on male consent to wear a condom.
Improved HIV infection
In February 2007, trials of a cellulose sulphate called Ushercell
were stopped ahead of schedule after women who used the gel were found
to run a higher risk of HIV infection compared with those who used a
dummy look-alike, or placebo.
Cellulose sulphate is based on an HIV-blocking sticky molecule
derived from cotton.
Carraguard uses the same blocking method, called HIV entry
inhibition, but is a different molecule.
In the same category as Carraguard are PRO2000 and BufferGel, being
tested in three trials in eastern and southern Africa, whose results
are due in 2008 and 2009 respectively.
However, last week the PRO2000 trial was scaled down, as it was
found that the higher-strength formulation of the cream was found to be
ineffective. A lower-strength formulation is still being tested.
In 2000, tests of an over-the-counter spermicide, nonoxynol-9, found
that it amplified, rather than reduced, the risk of HIV infection. The gel
apparently caused vaginal lesions that made it easier for the virus to
enter the bloodstream.
Ahmed said the encouraging safety results of Carraguard would allow
it to be used as a vehicle for future products, such as a gel that
would incorporate an anti-retroviral drug to kill the Aids virus.
An estimated 33.2 million people, in a range from 30.6 to 36.1
million, are living with Aids or the human immunodeficiency virus (HIV)
that causes it, the specialised UN agency UNAIDS says.
South Africa has become a key testing ground for strategies against
the global Aids pandemic. It has 5.5 million people with HIV or Aids,
the highest number of any country in the world. - (Sapa/AFP)