It is possible, just look at countries like North Korea, who are doing it all the time. Or Turkey, who are blocking unwanted sites, China, Iran, etc ...
Everything is possible. But why?
They will first vaccinate the usual 50-60% of sheeples, maybe also 70%.
And if really the great dying starts, well, they'll attribute to mutations.

And don't forget, for most of us there will be covid passports, which they can easy use to blackmail the non-vaxxinated.