If they are mutating that much, that fast, even a vaccine isn’t going to be very useful. And if they do indeed mutate to the point where one strain won’t protect you from the others, we may have to simply learn to live with coronavirus the way we do cancer: one of those ways you might die. Like cancer, only way faster.
I think a better analogy would be living with Polio, before the vaccine.
These types of viruses (rhino, corona, flu, etc) mutate quickly the goal (If it can be said that viruses have a goal.) is to keep replicating themselves to keep the “strain family” alive in a maximal way. So being immediately or near term lethal to the host is not in the best interest of the long term survivability of the strain. Making the host just sick or better yet asymptomatic increases the chances the strain continues. That’s the likely sweet spot it will go to. It’s not an absolute linear path there will upticks of lethality and it sucks if you catch that uptick but its eventually a dead end for the strain. I think this is why there is a very high number of asymptomatic cases and I bet that number will increase.