Abstract: The present invention relates to a shield for use on a prefilled hypodermic syringe assembly. The shield is intended to be retrofitable over a sheath/needle sub-assembly of the hypodermic syringe assembly in such a manner that insertion of the sheath/needle sub-assembly into the shield can be simply and easily accomplished by a medical worker, and subsequent extraction of the sheath from the shield is prevented by retention members which are formed from the housing of the shield, and which protrude into the chamber to hold the sheath. The retention member are formed so as to allow the sheath to be slidable into the chamber of the shield, yet engage the exterior surface of the sheath to resist extraction thereof once the sheath has engaged the retention members.