A distribution assembly having a syringe having a body with a tip supporting a needle having a bevel, and a removable syringe needle protection device. The protection device has a flexible cap defining an inside cavity defined by a side wall and by a distal solid end wall, and when in the protection position, receiving the bevel of the needle in airtight manner. The side wall includes an annular bead provided with at least one slot extending across the bead in a longitudinal direction, the bead, when in the protection position, co-operating in airtight manner with the tip of the syringe. The cavity of the cap is dimensioned so that when the protection device is removed from the syringe, the cavity is connected to the atmosphere via the slot before the bevel of the needle becomes connected to the cavity.
