My dog lost his hair too, around the injection site and my vet said it was my fault, and that the fur would grow back once he was feeling better. He still has that triangle of fur missing on his rump, and I will always ask for diluted rabies shots from now on. I have found that Benadryl is good for almost everything that ails a dog.
We adopted a 6 week old chihuahua, Max(his mom is a rescued miniature chihuahua, father is not known). Max weighs about 2 pounds. His first vaccination was given between 6 and 7 weeks. A friend gave him the 7 in 1 vaccine. After about 4 hours, I noticed swelling on Max's whole neck, and it was very tender (no swelling around his throat). Called a friend who works with a vet, she said to give him children's Diphenhydramine, but wasn't sure of the dosage. I gave Max 1/2 ml of liquid Diphenhydramine, (Children's Benadryl) repeated the 1/2 ml dose 3 hours later. I gave him another 1/2 ml dose 4 hours after the 2nd dose. By this time the swelling had gone down some, he seemed to feel better, but I just wanted to be sure he was going to be ok. By morning, the swelling was gone, he still has a little bump where the injection was done, but other than that, he seems fine.
I have a 6 year old Rat Terrier. After recieving her yearly rabies vaccination booster she started having adverse reactions to it. It started with a lot of scratching, and with in a few days to a week a small bald spot appeared with a small lump under the skin, about the size of a quarter. I have had a few friends whose dogs have completely lost all of their hair and regularly have scabs or sores where they recieved their injection, so I knew right away what it was. I as soon as I noticed the missing hair and felt the lump, I took her into the bathroom and washed her from head to paws with a medicated shampoo to rid her skin of any bacteria, dirt, or possible allergins. To prevent her from scratching I spray the area with a cortizone several times during the day, (this is something you can buy at the local pet store) and stop her from messing with it anytime I notice. On days that the itching seems more severe I give her a 25mg benadryl tablet and it does what I need it to do. When I think about it, I gently roll the lump between my index finger and thumb, and I also "snap" the skin a few times by pulling the lump away from her body and allowing it to snap back. This increases blood flow to the area and helps the body deal with the issue. I do these things just a few times, so I dont aggravate her or the area. So far the lump hasnt gotten any bigger, and the hair loss is only localized to that one little spot. I am happy with the results I have seen in her, the lump still isnt completly gone, but its doing much better. Her hair hasnt started to grow back either, but I figure a quarter size bald spot is better than no hair at all. I still continue to bathe her several times a week, but now I am using a oatmeal based wash. It much easier on her skin than continually using a medicated shampoo, and it seems to help with the all over itching as well. I wish you all the best of luck if you run into the same issue. I'd reccomend taking you dog to the vet if the lump continues to get bigger, if your dog gets hives, a temerature, or starts losing hair all over. I have a friend who has a toy Chiuaua and he had a severe reaction. She waited too long and didnt treat him herself so now he has open sores regularly and is hairless. By the time she got him to the vet there wasnt much the vet could do for him. They gave him a cortizone shot and some benadryl... two things anyone can do at home. I hope this helps some one, and once again good luck!!