Seal system for cannula

A method of transferring fluids between first and second containers, the method comprising:

• providing a needle hub, a cannula received by the needle hub, and a cannula seal enclosing at least a portion of the cannula, the cannula seal having a first position where the cannula seal encloses a distal end of the cannula and a second position where the distal end of the cannula is positioned outside of the cannula seal, the cannula seal having an open proximal end and a distal end, the distal end of the cannula seal including a rounded head portion;
• securing the needle hub to the first container;
• attaching a vial adapter to the second container, the vial adapter having a vial seal and a body, the vial seal being configured to engage the cannula seal, the body of the vial adapter being configured to engage a septum of the second container;
• engaging the vial seal of the vial adapter with the cannula seal via a rounded concave recess on the vial adapter that is configured to receive the rounded head portion of the distal end of the cannula seal, and piercing the cannula seal and the vial seal with the cannula such that the cannula is in fluid communication with the second container, the cannula seal moving from the first position to the second position;
• transferring fluid from the second container to the first container;
• and
• withdrawing the cannula from the second container and disengaging the cannula seal from the vial seal of the vial adapter with the cannula seal returning to the first position.