Plenty it appears and it’s nothing to do with virology, merely the law.
Aside from the medical profession where there is already precedent for insisting on vaccination for some clinicians - hepatitis. There is no other profession (that I’m aware of) that has vaccination as being an essential prerequisite for employment. Therefore any business wishing to change the contracts of EXISTING employees to make COVID vaccination mandatory as part of their contract of employment, would have to do so with consent i.e. the agreement of the employees concerned. Any attempt at ‘sign or leave’ would result in legal challenge imo.
An employer making COVID vaccination a prerequisite for NEW employees is up to them imo, if you’ve made a decision not to have the jab, then you won’t be applying. Not complicated really.