The invention relates to an adaptor for coupling with a medical container, closed by a septum having an outer surface directed towards the outside of the medical container, the adaptor comprising:- a gripping member (20) for securing the adaptor to the medical container,- a needle access port intended to face the outer surface of the septum when the adaptor is coupled to the medical container,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. The invention also relates to an assembly comprising such an adaptor and a medical container, and to the use of such an adaptor and of such a pierceable elastomeric piece for preventing the contamination inside a medical container closed by a septum.
