Earlier quoted context omitted.
All the more reason to stop all strains as soon as possible. If more contagious strains can be knocked below the sustainability threshold then they'll die out too.
It is not possible to stop all strains. SARS-CoV2 has multiple zoonotic reservoirs, transmits easily, and persists in the population via asymptomatic infection. We have eradicated one human virus in all of history, and it took a highly effective vaccine and a hundred years. The long tail is very long.
That immunity will likely be durable for many years (based on the somewhat recent study of HCoV-229E).
That will force the virus to mutate to achieve true escape immunity (a strain, not a variant, which can reinfect everyone all over) which will likely come at a cost to fitness, since one or two mutations to spike isn't enough, and there will need to be a few tens of mutations to spike.
That virus strain will not be as transmissible or virulent as what we are dealing with now, because it has had to make those costly "decisions".
And this is important for people who for medical reasons cannot be vaccinate or who are at high risk even if they are vaccinated. They're much better off being infected by subsequent strains down the road than being infected with version 1.x of this virus.
This is also what has been observed in the past with 1918 H1N1 which later evolved into seasonal influenza.