How is one supposed to know who isn’t vaccinated without violating medical privacy laws? (Not that laws are important to bolsheviks.)
They don't really need to know. They will just harass everybody. That is the whole point of the exercise anyway.
The COVIDIAN "faithful" will obediently show proof-of-vaccination and send the missionaries over to their heretic neighbors. It is, in effect, a renewal of their faith for both parties.
Households where the missionaries find objections can be marked for later attention by more energetic minions of the One True Faith of the State (tm).