The long-awaited trial that plans to answer whether a contraceptive injection increases a woman's risk of contracting HIV is set to begin this month. Since 2012 scientists have debated whether the progesterone injection, the most commonly used contraceptive in sub-Saharan Africa, may make women more susceptible to the virus. Some trials suggest it does. The hormone was used to make chimpanzees more likely to contract simian HIV during animal trials.But the evidence is not conclusive."We don't have a scientific answer," said one of the lead investigators, Professor Helen Rees, from Wits Reproductive Health and HIV Institute."The concern about the injection's risk remains an important question to answer as scientists have not cracked why so many young women become HIV-positive."Following a high-level meeting of experts, the World Health Organisation decided in 2012 that it still endorsed the injection as an effective family planning option, but it must be offered with condoms."There continues to be robust scientific debate about what we know and what we think we know, which makes the trial all the more important and necessary," said Mitchell Warren, director of HIV advocacy NGO Avac.About 60% of women in sub-Saharan Africa use injectable contraceptives because they only require a shot and a trip to the clinic every three months.The trial - which will take place over three years in Swaziland, Zambia, South Africa and Kenya - was due to start earlier this year but was delayed by tender processes and ensuring all four countries had the same contraceptives from the same manufacturers.The women in the trial are HIV-negative and will be coached to remain that way, but scientists will follow them over three years to see if the groups who get the injection have higher rates of infection.Hormones alter women's genetic make-up and scientists believe progesterone could make the vaginal wall thinner and more susceptible to HIV.Pfizer, maker of the injection, has repeatedly stated trial data does not show it poses women any increased risk of HIV...