The truth is, a Lepto shot is NOT considered to be a Core Vaccine, according to the American Veterinary Medical Association (AVMA).

Technically Leptospira a spirochete, a corkscrew shaped bacterium; Lepto is not a virus like parvo or distemper

This means the injection given to prevent an infection with this organism is not really a vaccine, but rather a bacterin.

Unlike a true viral vaccination, bacterin vaccines like lepto do NOT prevent infection; they can only decrease the severity of symptoms.
Further, bacterin vaccines can be shed in the environment, potentially infecting your other dogs, wildlife, and you.

Worse, not only does the shot fail to actually prevent the disease, but because symptoms are merely lessened, you may not notice that your dog is ill. You might think it just has some minor disorder, which you assume will pass, which means the infection will slowly brew, possibly causing permanent bodily harm. (Without early detection, Leptospirosis is very difficult to treat.)

One more factoid: the lepto 'vaccine' doesn’t even last a year. A dog who is given this shot receives less than one year of (inadequate) protection and is thereby placed at great risk for vaccine-related illness.

Jack