And vaccine escape is non-binary as well. Variants able to do that may displace other variants, but be unable to push R0 over 1 in a largely vaccinated population. The "South African" variant B1351 can break through Pfizer, but it does seem to be controllable.[1]
A booster shot has already been developed, and I expect we'll be able to win the arms race against this virus.
Saying B1351 "breaks through" is just like saying the original strain "breaks through" Pfizer. Pfizer isn't 100% efficacious on the original strain, nor is it 0%. Same with B1351. Luckily for us, new strains are closer to 100% than 0%.
We've most likely already won the arms race against this virus. I'll take a variant booster if I'm offered one, but in a population where 60%-70% of the population is vaccinated and a good chunk of the rest have natural immunity I doubt any of the existing variants can spread. And if it does spread it is only a matter of time before there's enough immunity to push R0 below zero for all the existing variants.
An actual immune-escaping variant is going to have to do more than just a few mutations and will have to substantially change along 20 or so different epitopes of the spike protein, which will almost certainly come at a cost to fitness.
It probably will eventually do that and it'll become endemic, but won't be anywhere near as transmissible or virulent as it has been.
A booster shot has already been developed, and I expect we'll be able to win the arms race against this virus.
[1] https://www.medrxiv.org/content/10.1101/2021.04.06.21254882v...