The same rules of the road apply to reinfection. A repeat infection won’t necessarily come with the same symptoms, or the same level of contagiousness. In the most classical portrait of reinfection, the microbe is effectively identical; your body, with its memory of the bug, is not. That probably means you’re not “completely susceptible again,” says Angela Rasmussen, a virologist affiliated with Georgetown University.
Typically, a person’s second rendezvous with a pathogen will be much milder, and pose less of a transmission threat. Immune cells are able to mount faster and stronger attacks; occasionally, these quick-draw assaults are so powerful that the microbe is purged before it gets a second shot at infection. Other times, immune responses are too weak or sluggish to forestall infection entirely, but still strong enough to exterminate the interloper before it causes symptoms. Most people “have probably been reinfected with lots of viruses in their lives and not known it, because they didn’t get sick,” Barker told me.
Repeat tussles with the same pathogen can also come with perks. Immune cells glean more intel on invaders each time they meet them, and strengthen their skills for future bouts. That’s textbook immunology: a body learning from experience.