Interestingly, I'd never had a cold sore in my life, until a few months (possibly 4 to 6?) before I got ME. I was working in a filthy hospital at the time, and a number of the patients had cold sores at the same time. So I picked it up through normal social contact, which I didn't think was possible. Some sort of virulent strain? But I was also getting a series of Hep B booster vaccines at the time as well. So perhaps I had a combination of immune onslaughts going on at the time.