I agree... no outings till vaccines are done and two weeks after the final vaccine.
Here is Dr Dodds Vaccine Protocol:
DR. JEAN DODDS' CANINE VACCINATION PROTOCOL ? 2010
Maybe your pup thinks he sees his old owners (breeder) and is trying to find them... my older rescue/adoptees did this for a while. She knew we weren't her 'people' so anyone else was a possibility....