Inoculator’s incomprehensible speech (6)
I believe the answer is:
jabber
I believe this clue is a double definition.
'inoculator's' is the first definition.
(someone giving jabs or inoculations)
'incomprehensible speech' is the second definition.
(rapid or incomprehensible speech)
(Other definitions for jabber that I've seen before include "Indistinct talk" , "Talk fast like a monkey" , "jaw, senselessly" , "empty prattle" , "one that's given punch" .)