A catheter assembly includes a catheter adapter and an introducer needle. The introducer needle extends through the catheter adapter and through a catheter tube so as to assist placement of the catheter tube into a patients blood vessel. Blood flashback into the catheter tube and/or catheter adapter through an aperture in a side of the needle indicates when the catheter tube is within the blood vessel. After the catheter tube is placed in the blood vessel, the introducer needle is withdrawn. A primary septum within the catheter adapter blocks blood flow in a proximal direction past the primary septum. A secondary septum proximal the primary septum is biased so as to enter into the aperture in the introducer needle and plug the aperture while the needle is being withdrawn, thus blocking blood flow through the aperture after the aperture is drawn through the primary septum.
