> Viruses don’t always become attenuated (less virulent). When they do, it’s because there is an evolutionary selection pressure driving it. No such pressure exists for SARS-CoV-2. An example of this type of selection pressure would be a virus that is so virulent, it kills its host before it can be transmitted to another one. A virus is essentially a machine programmed to make more viruses. To do that, it needs to be spread to new hosts. So variants that are so virulent they kill a host before that host can pass it along, that is under negative selection pressure. The more virulent viruses won’t be passed on. But attenuated variants will. They are under positive selection. For SARS-CoV-2, this has never been an issue. This virus can be transmitted to a new host before an infected person develops symptoms. Even those who die from COVID are most contagious before they become severely ill.

https://mobile.twitter.com/angie_rasmussen/status/1441416013...

Viruses select only for transmissibility, nothing else. They do not select for virulence any more than any other number of factors that may or may not overall have an impact on transmissibility. To think a virus naturally becomes less virulent to become more transmissible ignores a raft of other factors such as its ability to generate viral load that the host spreads, its ability to evade host defenses, presymptomatic/asymptomatic capability of spread, etc. etc.

Numerous viruses throughout history have not become less virulent even over the course of thousands of years.