We decided against HIB because I was breastfeeding AND because I had never heard of the disease before. When I was little this vaccine didn't exist. Therefore noone I knew was immunized for it, and never in my 29 years of life have I heard of a case, met someone who had it, got sick from it, died from it. I know this is not the most scientific of reasons to decide against this shot, but it is what comforted us.
Does your LO get formula for the other feedings or do you express milk? I would think even with 3 breastfeedings a day that would be enough milk to protect your LO.
I figure, my mom never lost any sleep because I wasn't "protected" from HIB (she didn't even know what it was or that it existed) so I will not lose sleep that my son is not "protected" either.
ETA: I'm sorry, I misread your post and don't have any stats to offer.