Prefillable drug delivery device, comprising: - a housing having a longitudinal axis and at least partially receiving a needle hub, said housing being movable with respect to said needle hub between a retracted position, in which a distal end of said needle hub extends beyond the distal end of said housing, and a protection position, in which the distal end of said needle hub does not extend beyond the distal end of said housing, - a tubular barrel for receiving a drug, said tubular barrel being capable of being pre-assembled on said housing via its distal end so that at least part of said needle hub substantially closes the distal end of said tubular barrel, said tubular barrel being movable in translation and/or in rotation along said longitudinal axis with respect to said needle hub and to said housing, wherein said device further comprises sealing means (22, 31) actionable once said tubular barrel is pre-assembled on said housing, said sealing means being capable of going from an inactive state in which no sealing contact is present between said part of said needle hub and an inner wall of said tubular barrel, to an active state, in which sealing contact is performed between said part of said needle hub and the inner wall of said tubular barrel, wherein, in the active state of said sealing means, said tubular barrel is movable in translation with respect to said needle hub between a filling position, in which the tubular barrel may be filled with the drug to be delivered, and an end-of-delivery position, distally spaced with respect to said filling position, in which said drug potentially received within said tubular barrel has been substantially expelled from said tubular barrel via said needle. - a housing having a longitudinal axis and at least partially receiving a needle hub, said housing being movable with respect to said needle hub between a retracted position, in which a distal end of said needle hub extends beyond the distal end of said housing, and a protection position, in which the distal end of said needle hub does not extend beyond the distal end of said housing, - a tubular barrel for receiving a drug, said tubular barrel being capable of being pre-assembled on said housing via its distal end so that at least part of said needle hub substantially closes the distal end of said tubular barrel, said tubular barrel being movable in translation and/or in rotation along said longitudinal axis with respect to said needle hub and to said housing, wherein said device further comprises sealing means (22, 31) actionable once said tubular barrel is pre-assembled on said housing, said sealing means being capable of going from an inactive state in which no sealing contact is present between said part of said needle hub and an inner wall of said tubular barrel, to an active state, in which sealing contact is performed between said part of said needle hub and the inner wall of said tubular barrel, wherein, in the active state of said sealing means, said tubular barrel is movable in translation with respect to said needle hub between a filling position, in which the tubular barrel may be filled with the drug to be delivered, and an end-of-delivery position, distally spaced with respect to said filling position, in which said drug potentially received within said tubular barrel has been substantially expelled from said tubular barrel via said needle.