Abstract: Provided herein is a method for storing an emulsion-adjuvanted vaccine in a medical injection device having a lubricant coating, said method including the steps of: (a) providing a medical injection device having a barrel having an inner surface; (b) forming a silicone oil layer on at least a part of the inner surface of the barrel that is intended to be in contact with the vaccine; (c) carrying out an oxidizing plasma treatment of the layer so as to crosslink at least part of the silicone oil layer and form a lubricant coating; and (d) filling the barrel with the emulsion-adjuvanted vaccine. The invention also relates to a medical injection device obtained directly from this method and to the use of plasma-treated silicone oil as a lubricant coating.