Do we know of any viruses that we don't develop immunity to? (I don't know either way). I'm guessing that if we've never encountered a virus like that, then th

Do we know of any viruses that we don't develop immunity to? (I don't know either way). I'm guessing that if we've never encountered a virus like that, then the occasional person we've heard that "got it again" might be just a false positive, one of the two testing times.