You may be interested in this article in the
Washington Post, about as Obama-friendly a newspaper as there has ever been. It cites people like Director of National Intelligence James Clapper and FBI Director James Comey among those warning that there is precious little information to obtain on anyone claiming to be from Syria seeking refuge.
There is nothing "thorough" about the vetting available, in short. There is no way to obtain information about these people from the Syrian government (not that even a majority of "Syrian" "refugees" are actually from Syria -- the phrase "Syrian refugees" also includes people from Mali, Tunisia, Ghana, Somalia, Yemen, Iraq, Bangladesh when used to discuss the horde sweeping into Europe and from which the US is supposed to start skimming), because we have no access to it if it even exists, and our own intelligence services won't have information on them unless they have
already been up to no good rather than obvious plants like those who participated in the Paris attacks.
Can we interview them? Yes. Can they lie? Yes. The good guys have to be right 100 times out of 100 to prevent an attack, the bad guys have to be right once.