My obs and GP (2 different people) said that it was fine to have it in the 2nd trimester. I just managed to get it in the 2nd tri - as was nearly in 3rd tri by the time I had it. So I had mine done as I usually have it (I'd rather not have to take time off school as it's too hard to write relief lessons for secondary school.) I've already had a bit of a nasty cold this season (early) and didn't fancy getting an actual case of flu to go with it.