It's been the opposite for me - I've been sick far less than usual since moving here. I think that has to do with moving from the city to the country, though, maybe. Less pollution, fresh sea air, and all of that. Plus, the weather does change frequently, but not from one extreme to the next, as it often does in Texas through the winter.
I did get incredibly sick the first time I came to England, when I stayed in London for a week. And there are others on the forum who have complained of frequent or long lasting colds and illness since moving here.