Catholics in Greece are overwhelmingly Orthodox. The Orthodox Catholic church distributes holy communion differently, with a spoon (there is a particular term for it, but I don't know it) that doesn't touch the communicant's mouth. So, they're not drinking from a communal cup.
It's entirely possible for the communicant to exhale / cough / sneeze on the spoon. I don't know what the priest would do if this were to happen.
As an aside, it's widespread right now (but maybe not universal) in Catholic dioceses to not even provide the cup to the congregation during Communion (which is perfectly fine according to Catholic theology btw). edit: additionally, I recently heard about a dispensation in at least one diocese for people who are in any of the COVID-19 risk categories that they don't need to receive Communion for now. I don't know whether this also dispenses them from attending Mass on Sundays (which is otherwise an obligation for all Catholics).