[jagraff]

Movement without energy is possible due to diffusion. Imagine you had a room with cellophane separating one side from another. Each side has a different gas, but both gasses are at the same pressure and at room temperature. Then, the cellophane is removed. Without adding any energy to the system, these gasses will mix until the whole room is a perfect mixture of the two gasses, simply because they both diffuse through the entire room. Something similar happens to allow viruses to move through your body (and, if they can be aerosolized, through the air).