A vial adaptor can include a connector interface and/or a piercing member. The vial adaptor can include a regulator assembly. The regulator assembly can include a regulator base, a regulator nest coupled with the regulator base, and/or a storage chamber formed at least partially by one or both of the regulator base and regulator nest. The regulator assembly can include a cover connected to one or both of the regulator base and regulator nest and fitted around a radially outward portion of one or both of the regulator base and regulator nest. In some cases, the regular assembly includes a flexible enclosure connected to the regulator nest and configured to transition between a contracted configuration and an expanded configuration. In some cases, the flexible enclosure is inhibited from transitioning to the expanded configuration prior to removal or modification of the cover from the regulator assembly.
