I dont think so, some brands like hygetropin are vacum sealed. I have used a ew diferent brands and I think the most important thing is that the GH is kept cool.
Prerequisite not necessarily but if the oxygen is removed it reduces oxidative degradation. This may not make a difference if the peptide is newly synthesized but over the long run it could.
Vaccum seal though is probably more important in the information it conveys. If your vial is not vaccum sealed well that could have occurred at the manufacturer BUT it could be the resort of someone buying in bulk and "rebottling" for resale.
A vaccum seal almost always rules out the latter possibility.
Why is the latter possibility bad? Handling, exposure to air, weighing... peptides are fragile and you lose a portion every time they come in contact with surfaces (even the glass of the vial & barrel of the plastic syringe) so having some fool who just picked his nose after eating a mouthful of potato chips scoop out some bulk peptide weigh it and put in a vial before crimping is not a good idea. :od-smil