The present invention relates to a prefillable drug delivery device (1), comprising :- a housing (10) receiving a needle hub (20) movable with respect to said needle hub between a retracted position and a protection position,- a tubular barrel (30) intended to receive a drug, and pre-mountable on said housing so that said needle hub closes its distal end,said device further comprising sealing means (22, 31) actionable once said tubular barrel is pre-assembled on said housing, capable of going from an inactive state where no sealing contact is present between said needle hub and said tubular barrel, to an active state, in which sealing contact is performed,wherein, in the active state of said sealing means, said tubular barrel is movable in translation with respect to said needle hub between a proximal position and a distal position, for realizing delivery of the drug.
