By Maggie Fox, Senior Writer, NBC News A once-a-day pill can protect people who inject drugs from the AIDS virus, lowering their risk by nearly 50 percent, researchers reported Wednesday. The findings show that even people at the highest risk of being infected with the virus can protect themselves – and thus protect others. And it adds ammunition to arguments that HIV drugs should be made widely available to fight the epidemic that has killed more than 25 million people. The study, published in the Lancet medical journal, demonstrates the value of pre-exposure prophylaxis, PrEP for short, the researchers say. “Our trial is the first evidence that PrEP can reduce HIV risk among people who inject drugs,” said Dr. Amy Lansky of the Centers for Disease Control and Prevention. “It does become another strategy that we have to use in preventing HIV in this population,” Lansky said in a telephone interview. PrEP has already been shown to protect people who are infected sexually, by far the most common way that the AIDS virus is transmitted. Doctors believe the once-a-day pills stop the virus from infecting immune system cells. “This is an important study,” said Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases, who was not involved in the study. “There were people who said you couldn’t treat injecting drug users at all.” .