The invention relates to an adaptor for coupling with a medical container closed by a septum, the adaptor comprising:—a gripping member (20) for securing the adaptor to the medical container,—a needle access port intended to face an outer surface of the septum,—a pierceable elastomeric piece (50) having a longitudinal axis located into the needle access port, said pierceable elastomeric piece having a recess (51) with a proximal opening and an outer wall (54) in contact with the needle access port,—attaching means for maintaining the elastomeric piece into the needle access port. The invention also relates to an assembly comprising such an adaptor and a medical container, and to the use of such an adaptor for preventing the contamination inside a medical container closed by a septum.
