Hello, Welcome to HCM, As your son was bitten by your pet vaccinated dog and also previously vaccinated against rabies with three shots of anti rabies vaccine. Dog is a known reservoir of rabies virus and can transmit rabies by biting, which is 100% fatal but 100% preventable by proper and adequate treatment. your son will be identified has Re-Exposure according to WHO categories and he requires two shots of anti rabies vaccine on days 0 and 3. Day 0 is the day of first of anti rabies vaccine. I would suggest you to consult your doctor for taking these two shots of anti rabies vaccines. Thank you.