A closure system for a vial comprising: an elastic closure part to engage the mouth opening, a clamp part to hold the closure part in a closing relationship with the mouth opening, the clamp part defining an upper aperture through which a region of the upper surface of the closure part is exposed when the clamp part is engaged with the vial, a cover part to engage the clamp part to cover the exposed region, the cover part engaging with the closure part to provide two or more concentric ring-shaped seals, at least part of the cover part being removable from the vial to allow access to the closure.