If the current "vax" does not prevent the "Delta" variant, then how do the un-"vaxxed" contribute to "Delta" variant "outbreak"?

Even though the current "vax" offerings do not prevent "covid" transmission as per their respective inserts, the latest narrative is that the un-"vaxxed" are somehow responsible for this new "Delta" variant, but the logic of this more recent spin campaign does not hold up whatsoever.