A needle assembly (10； 210) for a prefilled injection syringe is described. Aneedle holder (12； 212) has a needle (14； 214) secured to it and is adapted tobe secured to a syringe barrel of the injection syringe. A needle sheath (16；216) has a distal end forming a releasable sterile seal with the needle holder(12； 212), and surrounds and shields the needle (14； 214) . A needle seal (18；218) surmounts the needle tip and is arranged at least in part in the proximalend of the needle sheath (16； 216) and closed off by a closure element (20；220) . A closure connection between the closure element (20； 220) and theneedle sheath (16； 216) is configured as a non-releasable and sterile barrier(54； 254) produced by means of bonding or welding.
