If you let any pathogen just go through the human population with little reaction, the pathogen has little pressure to engage in mutation driven evolution that adapts to the reactive measures. On the other hand, if you try mightily to suppress a pathogen, you are just asking for it to figure out a way to defeat whatever suppression measures you take. Every virus mutates constantly, generally in random directions across its sequence. Errors in transcription, external factors affecting accuracy of sequence copying, etc. lead to many, many changes. Most don’t have any functional meaning, some may be harmful to virus replication and expansion. But some may prove advantageous, allowing the virus to transmit more easily, to get inside cells more quickly, to evade immune responses, and so on. CV-19 may be differentiated from other coronaviruses by an evolution to a stronger receptor binding. In our general stupidity of not thinking through reactions to this virus, we are ignoring the likelihood that we are creating selective evolutionary pressure in a way that makes this virus more infectious and/or more lethal.
A study of virus mutation and emergence of modified strains in Houston found that a particular single-base pair substitution had quickly become the dominant strain in that area. (Medrxiv Paper) Other scientists have found the same mutation. While some have hyped this as dangerous, that may be an overstatement, but it does appear that the new strain may be more infectious, primarily by leading to higher viral loads in the upper respiratory tract and greater ability to infect target cells. According to the Houston paper this may be due to the mutation aiding in avoidance of a neutralizing antibody and faciliting the spike protein fusing with the target cell membrane. Interestingly, the variant did not appear correlated with outcomes, but Rh factor positive blood type and age were.
We shouldn’t be surprised if our ongoing efforts to suppress this virus result in other mutations making it more threatening to humans. Sometimes it is best to leave well enough alone. And those suppression efforts are probably giving children weaker immune systems against all pathogens, including CV-19. Nice work, so-called public health officials.