I'm not sure what the studies are, and I know my experience is only anecdotal and just one baby, but my DD (who is still bf) seems to suffer from the same colds that her little friends get, but with a lot less intensity, they last for much shorter periods and have never gotten beyond the cold stage (where her little non-bf friends end up on antibiotics). So in our case, she still gets sick and catches the bugs off her friends, but not as bad.

I'm hoping she bfs through this winter since she's going to start preschool soon!