Viruses often mutate over time.
Yes they do. But why push a vaccine (I was asked at my physical if I wanted it) if it’s not contagious? If there’s no need for isolation - and even with the flu they want you symptom free for 24 hrs - then does the risk outweigh the benefit of getting vaccinated every 3-4 months with an ever changing formulation? Risk vs Benefit, it’s really that simple…for all drugs.