It's not a threshold. For getting infected, it's like lottery tickets. For severity of infection, a bunch of "winning" lottery tickets make it difficult for y

It's not a threshold. For getting infected, it's like lottery tickets. For severity of infection, a bunch of "winning" lottery tickets make it difficult for your immune system to catch up. Getting a large exposure is like giving the virus multiple viral generations of a head start without being noticed by the immune system.