For a few dozen people in the world, the downside of living with a rare immune condition comes with a surprising superpower—the ability to fight off all viruses. Columbia immunologist Dusan Bogunovic discovered the individuals’ antiviral powers about 15 years ago, soon after he identified the genetic mutation that causes the condition. At first, the condition only seemed to increase vulnerability to some bacterial infections. But as more patients were identified, its unexpected antiviral benefit...