I'm talking of the virtual EM modes of vacuum...
You've missed the point @Vanadium 50 was making. For any EM mode to be polarized, it must be polarized in a particular direction. That means that particular direction is different from other directions. But in the vacuum, all directions are the same; they have to be, because it's vacuum, so there is nothing there to pick out a particular direction. So virtual photons in the vacuum can't be polarized, because if they were, it would violate the property of the vacuum that all directions are the same.How can I expect a direction when I don't even know if it is possible for Virtual photons to have circularly polarized modes?