hi and welcome you could vaseline to do the trick good luck.

at this time of year i tend to leave the cut to dry by itself with out any fungal risks. but vaseline will do the trick as would molten wax from a small candle.

welcome to GoY from me to.

About where do you garden, Jen? We use water-based asphalt emulsion here in the States, but that is mostly to stop insects that don't occur in Europe.

Self-healing is always best, as seaburngirl says. Not aware of vines getting bugs through a cut, though they might die-back to a sprout, shoot etc. Vine usual problems are insects that sap or eat the leaves. If you are really concerned, then go for a natural heal, such as beeswax (an idea I have picked up from a tree surgeon for healing grafting wounds).