Does that not assume that you’re symptomatic at the same time you’re spreading the virus? With covid you appear to be able to spread before you know you have it

Does that not assume that you’re symptomatic at the same time you’re spreading the virus? With covid you appear to be able to spread before you know you have it. Given that, what force would cause the virus to be selected for less lethality? With a different presentation of disease where symptoms and spread occur concurrently then there would be a pressure on the virus selecting for strains that arent so lethal a carrier has no chance to spread. In covid’s case, that pressure doesn’t exist as far as i can see?