Dog scratched with teeth. Or not.

I have adopted a stray dog who was badly wounded by a domestic dog. I have cared him alot and also given injections for his injury but not a rabies one yet because he was having too many injections everyday that it was hard for him to have that much pain. It is now about 3-4 weeks that he is with me. But today, when i was attaching his chain around his collar, he tried to bite me, but i saved myself. There was no wound but the skin is very little scratched, and i think there was a little blood around that scratch for 2-3 seconds. I washed that scratch thorouhly with soap. I am just curious whether to get a vaccine or not because that scratch is very small and completely invisible. Please help me Sir/Mam and let me know whether to get a vaccine or not.