Where do these new variants come from?
Coronaviruses are fast mutaters. Not as fast as flu but still fast. Now that the virus is loose, it will constantly evolve alongside us just as it has done with bats and just like the flu has done with us. Whatever adaptations it gains via mutations that promote its reproduction will be naturally selected for. We see this as increasing affinity for the ACE2 receptor primarily but there are certainly other adaptations that it could acquire that facilitate its reproduction-like not eliciting a fever for example or even avoiding detection in PCR tests. It will adapt to every countermeasure we throw at it in this way because that’s what viruses do and when they do it rapidly, it’s a problem.
When two variants love each other very very much, they, well, kiss and produce a baby variant...
Viruses will mutate, at times they may become more harmful and at other times less harmful.