I cant remember who asked as im getting sleepier but breastfeeding has been shown in studies to improve the responce to vaccines. However if you take the view of many of us, BF is the normal way to feed so artificial feeding decrease the responce. There was a resent article in Pediatrics on this.
Breastfeeding does not contraindicate receiving vaccines.
For vaccine info/contraindications see the CDC's web page
-Rob
Gloria, you knew I'd respond to this didnt you?