A needle assembly adapted for fluid communication with a vial containing a substance to be delivered to a subject, the needle assembly including a needle held in a needle holder, the needle holder confined to move in a housing, and an activation mechanism for activating delivery of the substance through the needle, the activation mechanism including a safety latch that initially impedes movement of the needle holder, wherein when the safety latch is placed on the subject, the safety latch moves to a position that permits moving the needle holder to cause the needle to protrude outwards of the housing to pierce the subject to allow administration of the substance to the subject, characterized by a biasing device arranged to apply a biasing force on the needle to cause the needle to protrude outwards of the housing to pierce the subject, and needle release apparatus including a needle arrestor that initially blocks movement of the biasing device and which releases the biasing device when the safety latch moves to the position that permits moving the needle holder to cause the needle to protrude outwards of the housing.