Like many heroin addicts, Patrick Schnur spent his youth in the revolving door of rehabs and treatment facilities. He'd tried everything to kick his addiction: Suboxone, a drug used to wean addicts off of opioids, and Vivitrol, a monthly injection to relieve opioid cravings. He'd tried therapy and in-patient treatment programs. He'd stay sober for a few months, then relapse again. Each time something seemed to work, suddenly, it wouldn't.

Just before he relapsed for the last time in December, his parents Kathy and Dennis Schnur learned about something else: a vaccine, which could numb him to the effects of heroin and prevent him from overdosing. Patrick was doing well—had been sober nearly two years at that point—but they knew better than to consider him cured. The vaccine was still in development, but they thought if they could just get their hands on it, then maybe they could breathe easier, stop worrying every time the phone rang.

But then the phone did ring, and it was too late. No one knows why Patrick decided to use again, other than the strong pull of addiction and perhaps the desire to celebrate—he'd just completed his first semester of pharmacy school with a 4.0 GPA and his life finally seemed back on track, after years of spiraling out of control. The next day, he was supposed to fly to see his parents for Christmas break. He never made it on the plane. By the time they found him in his dorm, he was gone.

Watch: Inside America's Opioid-Fueled Epidemic

These are the stories Kim Janda thinks about when he shows up each morning to his lab at the Scripps Research Institute in San Diego—the Philip Seymour Hoffman-type stories, where someone seemed to be doing so well, maybe stayed clean for a few years or even decades, and then in an instant, got pulled under. It's not just that the stories are harrowing, heartbreaking; it's that they're so common. The relapse rate for heroin and opioid addicts is, according to some research, nearly 100 percent.