The human body will continue to evolve. When there are many germs around, the human body must improve its defense ability if it wants to survive, not die and not lose the activity of cells. The human body carries a lot of germs, which makes the immune system have a backup. The next time an effective pathogen enters the body, the immune system can quickly play a role in killing the pathogen before it really reproduces. So now we rarely encounter the ancient plague phenomenon, and now novel coronavirus is also a challenge brought by the constant evolution of viruses.
At present, there are a large number of viruses and bacteria in the human body, which is equivalent to a biochemical weapon. However, in such a modern society, everyone has about the same number of bacteria and viruses and will not affect each other. However, if a modern person really travels back to the Song Dynasty or the Tang Dynasty, then this person is a biological weapon, and he will cause environmental changes, because some germs he carries should not be in that dynasty.
Britain even put forward some kind of evolution, that is to say, as long as everyone is infected with this virus, antibodies can be automatically backed up by the human immune system, and most people will be fine, only a few people will die because of this virus, but some defensive measures have been taken later. After all, it smells good, and no one can escape. Whether to cure this kind of thing or not depends on the immune system.