I agree with
@Superveloce in that people will travel to where the passports aren't needed.
However...the airlines can start putting in the requirements and control the travel in that way. No vaccine, sorry you can't get on our flight because we'll get sued for getting someone else sick/killed/hospitalized.
If the borders close up, there are other ways to control this. Plus...if Italy puts in a passport requirement...that means all of the EU has a vaccine passport requirement.
As for the planes coming in from hot spots to Canada....ridiculous. Total and utter failure by Canada to stop this.
You, Mr. Greece, want money from the world wide bank? No problem...implement a vaccine passport requirement.
There are ways...someone just has to implement / enforce it.