If the Biophage really makes another appearence all the Klingons have to do to profit from it is to do nothing and attack after the threat is dealt with/contained which is not something Starfleet has the right, ability or even willigness to sanction/act against, esepcially consideirng the power of the Klingons.
The Federation will not appreciate this apparent biowarfare strike by the klingons. At best it will sour relations.