I think people think vaccine escape is achieved in one Big Bang. From what I’ve read it’s more like successive variants wear the vaccine resistance down that’s why you want to stop variants occurring.
I don't think that variants wear down resistance.
Vaccines don't really target a virus. They target a distinctive protein on the virus' shell--in this case the "spike" protein that lets the Covid virus breach the human cell. The vaccine contains (or, in the case of the new mRNA vaccines, manufactures) the target protein, which, when injected, provokes the body into creating antibodies that react to foreign proteins. Antibodies are like templates matched to the shape of the alien protein. They block these proteins and mark the virus for destruction by white blood cells. The body remembers how to make the antibodies after an infection. So you have protection for awhile, even for life.
But it is better than that. If something like 85 to 95% of a population has antibodies to a given virus, either because the individuals are vaccinated or have had the disease, that population has so-called herd immunity. Individuals susceptible to infection--those in the unprotected 5-15%--are isolated from other unprotected persons by the immune people around them. So the virus cannot jump to a new host. All else being equal, the virus will become extinct, like smallpox.
Unfortunately, viral proteins do not necessarily stay the same. The genetic material of viruses like Covid, colds, and influenza is prone to mistakes--mutations--during replication. So the more replications there are, the more variants there are. Each mistake/mutation makes it more likely that the target protein for a vaccine will change shape to the point where the antibodies generated by existing vaccines (or by previous infection) can no longer lock on to the target. This is why we get colds and the flu every year, even if we are immune to all the versions we've had in the past.
Needless to say, a large percentage of unvaccinated people--like the 30% resisters in the US and the millions that we have shortsightedly failed to vaccinate in Africa and Asia--makes rapid transmission, rapid viral replication, and new mutations much more likely than it would otherwise be. They create a "herd susceptibility" that greatly increases the probability that existing vaccines will lose effectiveness over time.
But loss of vaccine effectiveness may not be the only--or the worst--fallout from low vaccination rates: the unvaccinated may actually make the virus deadlier. Viruses replicate at a tremendous rate compared to, say, humans or elephants or trees. So natural selection acts on them in days and weeks rather than in millenia and eons. If uninfected hosts are few and far between or immune to a virus, then natural selection favors viral mutations that make the virus less virulent. Less virulent variants replicate less aggressively and make less virus, but their hosts live long enough for the virus to spread and reproduce in a new host. But if uninfected hosts are readily available and unvaccinated, natural selection favors the most virulent mutations, the ones that replicate most aggressively and turn as much of the host into new viruses as possible. The host dies quickly, but a new one is ready to hand. You then have a deadly, runaway epidemic that wipes out the unprotected, which may well include those whose vaccinations have been rendered obsolete by mutations to the target proteins.
This is why the fate of each of us is the fate of all of us in this situation. Refusing the vaccine or denying it to others, in Africa or elsewhere, endangers all of us.
www.bbc.com
www.telegraph.co.uk
