Yes. Strangles vaccines do more to minimize the severity of disease than to prevent it. This is because of the way the bacteria attacks the body and breaks down the local/immediate defenses.
Does it have to be right at the jaw/neck? A friend of mine had a lump just below the jaw on the neck. We thought it was a bite (maybe last week) and now today it's split open and oozing. It is also hard. I asked her to take a temp.... (I know her horse is vaccinated...)