Although the HIV virus disproportionately affects women in developing countries, only about one fifth of participants in vaccine trials in most of Africa’s sites are women. Since women’s immune response to vaccinations could be different than men’s, scientists worry that the decreased number of female participants in their trials could result in a vaccine that won’t be as effective at combating HIV in women. “We could end up with a vaccine that we can only say elicits a good immune response in men. We will not know if it works equally well in women,” the director of a HIV vaccine development group in Uganda explained. Some HIV researchers speculate that women are less likely to participate in trials because — even as adults — they have to seek consent from their partners or parents, many of whom may not support the idea. Continuing to combat HIV stigma may encourage a greater number of women to seek out HIV vaccine trials and medical care.