No. That's not even remotely possible. In theory, the closest you could get is if you could design a virus that only really harmed people with some rare genet

No. That's not even remotely possible. In theory, the closest you could get is if you could design a virus that only really harmed people with some rare genetic variant, and that variant happened to be one that a person you wanted to target had. That's still pretty far out in terms of actual practice, but it's not so far out that it's crazy. Designer viruses that target one, single person is just crazy talk.