Can't understand the replies - surely it is the pup that is at risk, and even if the older dog is up to date with its jabs, it can carry infections and pass them on, just because it is jabbed doesn't mean the puppy won't catch something from it.
Having said that, most pups get some immunity from their mothers, and I have always brought pups straight into my house with my older dogs. I also consider lack of socialisation as more of a threat to a puppy than the possibility of catching something, so my pups go out and meet lots of people and animals from a very early age.