A medicinal vial stopper has a stopper plug extending from a stopper flange. The stopper plug is insertable with a compression fit in the neck of the vial. A first bore within the stopper plug has a radially inwardly facing first-bore surface having a constant first-bore diameter the entire first-bore length and a first-bore first end closed by a centrally-located piercable portion of the stopper flange. A second bore within the stopper plug has a radially inwardly facing second-bore surface having a constant second-bore diameter the entire second-bore length. The second-bore diameter is greater the first-bore diameter. The second-bore first end is in fluid communication with the first-bore second end. The centrally-located piercable portion of the stopper flange is resiliently deformable and upon being pierced by a spike tightly conforms to the radially outwardly facing sidewall of the shaft thereby forming a fluid impenetrable seal.
