And by the way, Covid-19 is so dangerous to people probably because it was in a bat vector. It's not in a virus' long-term interests to be deadly to its host, because that makes it harder to spread. Given the rapid mutation rate, that means it tends to get less deadly as it spreads.

Which is why the social media bollocks about it having 'escaped a Wuhan lab' might make a virologist laugh in your face. Ironically (unless they had been for some reason culturing it in bat cells), if it had escaped the lab it would be far less dangerous. Unless it was meant for warfare, in which case it a 3.5% mortality rate with 90% of the victims having poor health would be FAIL. Generally opposing armies aren't made up of people with diabetes and high blood pressure.

In cell culture, there's absolutely no need for a pathogen to have immunomodular proteins, virulence or indeed any other way to avoid the host immune system. And as they say, use it or lose it - mutants that saved energy by not having these things would soon outbreed the other variations and become the main strain which then can't survive outside culture. This can be a real problem for people who intentionally grow pathogens for research.