In one aspect, a safety pen needle assembly is provided which includes a hub having an open proximal end, a needle fixed to the hub having a distal end, and a shield moveably mounted to the hub so as to be movable relative to the hub to selectively cover the distal end of the needle. An interface is defined between the shield and the hub which is sufficiently sealed so as to define a sterility barrier which prevents ingress of contaminants through the interface. At least one sterility barrier is mounted directly to, and across, an open proximal end of the hub and an open distal end of the shield.