The delta variant already did this.

There is a strong selective pressure to escape the vaccines, it's just a matter of how large the space of functional escape mutations is and how quickly it can be explored. That space is of unknown size, but the speed at which it can be explored is directly proportional to population size, i.e. infection rates. In addition, the larger the population, the more likely that slightly deleterious mutations will survive long enough for a new optimum to be reached in subsequent mutations.

If every country had followed China's example, we'd at least have a low rate of new allele generation, possibly even eradicated it by now. Instead, we're playing with fire.

Source: took virology and lots of pop gen.