If the scientist is Stephen Hoffman, he takes a small can and fills it with three hundred irradiated mosquitoes. He inverts the can, placing the mesh lid against his bare forearm, and a cloth over his arm to simulate night. He begins to feel a tickling sensation. Three thousand bites later, he withdraws the can. He has “vaccinated” himself. Then, two weeks later, he repeats the process, only with infectious mosquitoes instead of benign ones, and . . . waits.