Microbicides: why are they significant? (Part 1)

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Microbicides: why are they significant? (Part 1)

20 February 2008

Ahead of next week’s biannual international microbicides conference Microbicides 2008 running 24 – 27 February in New Delhi we take an in-depth look at microbicides. In part 1 of this 2-part series we look at why they are considered significant in the response to HIV. In part 2 the challenges to the development of this biomedical prevention technology will be explored.

While the search for a HIV vaccine looks
set to continue for some years, many
believe that with similar investment a s
uccessful microbicide could be developed
much sooner.

With 2.5 million people newly infected with HIV in 2007 there is global consensus on the need for new HIV prevention technologies to complement existing strategies.

While the search for a HIV vaccine looks set to continue for some years, many believe that with similar investment a successful microbicide could be developed much sooner. An effective microbicide would offer significant protection to women who currently comprise about half of all people living with HIV worldwide.

UNAIDS works with number of microbicide networks to highlight the critical need for female-controlled prevention options.

Along with other global advocates, UNAIDS continues to emphasize the importance of a concerted effort to develop microbicides and make them accessible to the people that need them. Addressing women’s needs for HIV prevention is vital for curbing the epidemic.

Why do women need specific HIV protection?

It is an uncomfortable reality that many women across the globe do not have power over what happens to their own bodies.

Deep-seated social and cultural norms and the effects of gender inequality mean many women and girls live with violence or the threat of violence and are unable to successfully negotiate fidelity or condom use.

Women who sell sexual services are often unable to negotiate the wearing of condoms with their clients.

Even women abstained from intercourse before marriage and have only one sexual partner can be vulnerable to sexually transmitted infections from partners if that partner engages in unprotected sex with other women or men.

“Microbicides will be a key tool in
empowering women, and in halting the
alarming spread of HIV infection among
women” - Director of the Global Coalition
on Women and AIDS, Kristan Schoultz.
Credit: UNAIDS/C.Gira

Due to biological differences, in unprotected heterosexual intercourse women are at least twice as likely as men to acquire HIV from an infected partner. HIV data reflects this, for example among young people (15-24 years) in sub-Saharan Africa an estimated three young women are HIV-positive for every young man.

Experts believe if women have the option of using a microbicide to protect themselves from HIV it could make all the difference to their lives.

“A man may refuse to wear a condom and his partner may be powerless to insist. Access to safe and effective microbicides will offer women more choices and help them take charge of their sexual health and their future,” said Director of the Global Coalition on Women and AIDS, Kristan Schoultz.

“Microbicides will be a key tool in empowering women, and in halting the alarming spread of HIV infection among women,” she added.

What is a microbicide?

A microbicide is a compound whose purpose is to reduce the infectivity of viruses or bacteria. The term has come to refer to a potential product which would prevent the transmission of HIV and other sexually transmitted infections (STIs) inside a woman’s vagina. A rectal microbicide would act similarly to protect men who have sex with men and women during anal intercourse.

There are different candidate microbicide products currently under research and development; many are in the form of a gel or cream to be applied to the surface of the vagina. Scientists are also exploring other ways of drug delivery such as by a vaginal ring which would be inserted into the vagina and provide controlled release of an effective microbicide.

Mechanisms of action

A successful topical microbicide – applied to the vagina surface - would probably act in a combination of ways. Scientists are researching different products which would:

  1. Kill pathogens without damaging the healthy cells of the vagina
  2. Strengthen the body’s natural defence system by increasing the natural acidity of vagina inactivating athogenic viruses and bacteria
  3. Inhibit the virus getting into the white blood cells – the target cells of HIV
  4. Inhibit viral replication by using derivatives from anti-retroviral drugs

For some women, it is important that the action of the microbicide not impair their ability to conceive a baby. Both contraceptive and non-contraceptive microbicides are currently under development, as well as rectal microbicides for heterosexual women and men who have sex with men.

No silver bullet

The biannual international microbicides
conference “Microbicides 2008” will run
24 – 27 February in New Delhi under the
theme “Striving towards HIV Prevention”.
Credit: Microbicides 2008

Some advocates believe that the successful development of a microbicide would bring significant emancipation for women who due to cultural, economic and social drivers are disempowered and unable to protect themselves from HIV.

With the stakes so high, microbicides seem like a very attractive solution. However experts are realistic about the complexity of the research task and drug efficacy and urge caution over raising unrealistic expectations.

Successful microbicides products will be partially protective. Although they may be up to 80% effective in preventing the transmission of HIV during sexual intercourse, they would need to be complimented by other prevention tools in a combination prevention strategy.

A comprehensive HIV prevention package includes, but is not limited to, delaying sexual debut, mutual fidelity, reduction of the number of sexual partners, avoidance of penetration, safer sex including correct and consistent male and female condom use, and early and effective treatment for sexually transmitted infections.

In part 2 we look at the challenges in current microbicide research and development and explore why there is a large funding gap between what is needed to bring clinical trials to completion and lay groundwork for effective distribution and what is currently available. We also look at the ethical considerations of clinical trials.