Why do we need microbicides?

In 2010, South Africa launched the largest HIV-testing campaign ever conducted, with massive condom promotion and free condom provision as part of the campaign. Nonetheless, access to condoms is not enough to meet the HIV-prevention needs of women in South Africa and elsewhere.

Data from a rural clinical-trial site north of Durban, South Africa, shows that HIV incidence among young women is 4.4% a year, with no decline at all since 2003. While HIV prevalence in the community overall is 22%, over half (51%) of the women aged between 25 to 29 were HIV-positive in 2009. Condoms are available, but when researchers used multiple methods to collect condom-use data they concluded that actual levels of consistent condom use were 25% at most, half the rate that had been indicated by self-report.¹

If having condoms available ensured their use, women would not be getting infected with HIV at such rates. In light of such data, access to even a partially effective microbicide is an urgent priority. Moreover, recent mathematical modelling suggests that a 40 to 50% effective microbicide could prevent 1.3 million new HIV infections and 826,000 deaths in South Africa alone over the next 20 years.²

The need for a microbicide that can be used rectally by women and men having anal sex is also compelling. HIV is transmitted about ten times more easily rectally as vaginally, with a frequency (from partners with chronic HIV infection) of about 0.8% per act of intercourse compared with 0.08%.^3,4 Not only is transmission easier with anal sex, but some data suggest that heterosexual couples may be less likely to use condoms when they have anal sex than when they have vaginal sex (possibly because the risk of pregnancy is removed). Thus, anal sex may be a significant contributor to HIV transmission among heterosexuals, as it obviously is among men who have sex with men.

The worldwide role that heterosexual anal sex plays in HIV transmission is obscured by the lack of data. Discussion of anal sex among heterosexuals is almost universally taboo, largely because of the behaviour’s association with homosexuality. This taboo has severely limited access to funding for research to explore its real impact on HIV risk and transmission rates. It also discourages the self-reporting of anal sex in studies where it is explored.

In two of the microbicide trials recently conducted in Africa, about 2 to 3% of the trial participants reported having anal sex.

In a South African National Youth Survey of 11,904 people aged 15 to 24, 3.6% overall reported having had anal intercourse.⁵ Among the sexually experienced young men surveyed, 5.5% reported having experienced anal intercourse (of these only 0.06% reported having men as sexual partners). An equivalent number of female survey participants (5.3%) reported ever engaging in anal intercourse. The men reporting anal intercourse were 1.7 times as likely to be HIV infected as men reporting only vaginal sex, and men aged 15 to 19 years 4.3 times more likely. Both of these findings were statistically significant. However, no statistically significant association existed among young women between reporting anal sex and being HIV-positive. Even if the male/male sex in this survey was significantly under-reported, the data nevertheless suggest that anal intercourse may be a significant contributor to HIV transmission in South Africa.

In one American study of women “at high risk of HIV infection”,⁶ a third of the women had had anal sex. In another, researchers conducted telephone interviews with a sample of 3545 California adults (under-sampling those aged 44 and older).⁷ A total of 7% of all the sexually active respondents (8% of males and 6% of females) reported having anal sex at least once a month during the year prior to the survey. Of these, most engaged in anal sex from one to five times per month, and about 60% reported never using condoms. However limited, such data clearly speak to the need for rectal microbicides among men and women who have anal sex, regardless of their self-defined sexual orientation.

In the UK, 12.3% of male respondents and 11.3% of women who responded to the National Survey of Sexual Attitudes and Lifestyles (2000) reported anal intercourse with a partner of the opposite sex in the previous year.