DS had his MMR a week ago last Monday. The following Wednesday evening he threw up his dinner and was ill/sick for about the following 3/4 days - nothing major he could still eat toast/rusks and drink water, but anything else came back up. He's pretty much recovered from all that though is still a bit whiney and clingy.
At the time I thought it was a bug but (touch wood) no one else has caught it I'm now wondering if it was a reaction to the jab?
He also had his Prevenar jab (the new one - not even sure what it does - rubbish mother!) at the same time, so it could also be that...