Imagine if only half the population ever got the polio vax.
Viruses don't stop. They'll constantly evolve.
Science can only do so much.
Either be a host and help spread, by helping to create more vigilant super strains or....take a shot that'll give your body an advantage in fending off an attack.
They could go back and rework the vax and do away with the mrna versions, and make them old school way, and design them like the yearly flu(influenza) shot/vax/booster, only in this case for the different variants of covid, and make it just like getting a yearly flu shot - AND because of the zhitshow and mass dis-info that is the internet, and what has been spread about anything covid related - there'd still be a huge section of the population that wouldn't take a measly shot in order to help mankind as a whole.
As the whole planet keeps getting warmer year over year, and melting of glacial ice, and thawing of untouched tundra's and permafrost - we're gonna have untold amount of new viruses and bacteria being released into the atmosphere and water ways.
There's no reversing this.
Only thing that'll reverse the changes is mass depopulation, err, extinction.
Once the nuclear wars start and a nuclear winter sets in and the remaining people left in scattered pockets around the globe are reversed back to tribal hunter and gathers, then the planet will reverse the changes.