system
Given the following post, respond as if you're commenting on Reddit:
human
Why don't we always get immunity to diseases that we have had once before?
gpt
Lots of infectious diseases you can get multiple times because different strains exist, or mutate into different strains that is immune to the antibodies that worked on the earlier strain. Also some diseases like the common cold are actually caused by a bunch of different viruses that all prompt the same symptoms.