It is actually quite common for babies to be a bit off their feeds after vaccination, since they may be feeling sore or just generally unsettled from the jab. That said, if the reduced intake goes on for more than a day or two, or if he seems very lethargic or is running a fever, it would be good to bring him to see his PD just to be safe. You can also call KKH's 24-hour helpline if you are unsure and want a quick opinion without making a trip down. Most mums find things go back to normal pretty quickly once the baby recovers from the jab.