For seven years, a daily pill has been available in South Africa to protect people from getting HIV. But when Victoria Makhandule, a community health worker, counsels the young women in her township about the medication, they tell her it doesn’t work for them. These young women are among the most vulnerable in the world to HIV, the virus that causes AIDS, but they say the daily pills, known as PrEP, bring their own challenges. The women may spend an unexpected night away from home and miss a dose, or forget for a day or two.