Women are also becoming infected at a significantly younger age than men. On average, women become infected 5 to 10 years earlier than men. Seventy percent of all new infections in women are among 15 to 24 year-olds. Women are biologically more vulnerable than men to HIV infection. Studies have found that male to female transmission appears to be 2 to 4 times more efficient than female to male transmission, in part because semen contains a far higher concentration of HIV than vaginal fluid.
Young girls are particularly vulnerable.
The economic, social and physical power imbalance between men and women contributes to the lack of safety in sexual relationships and the difficulty for many women in negotiating safer sex. To do so may have serious repercussions, ranging from stigma to fear of violence or abandonment. The power differential between men and women is compounded by age differences. Women typically marry or have sex with older men, who have been sexually active longer and are more likely to have become infected. Any non-consensual or coerced penetrative sex can carry an increased risk of HIV transmission, particularly as men are not likely to use condoms in these situations.