These vaccines are useful for administration to humans and other animals at risk of {HEAD ~ exposure} to {TAIL ~ C.} difficile toxins 
to
These vaccines are useful for administration to humans and other animals at risk of { HEAD ~ exposure } to { TAIL ~ C. } difficile toxins
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH