Prevention. Commercial vaccines are available and protect against clinical disease associated with the L. icterohaemorrhagiae and L. canicola serovars. Inoculation does not, however, prevent infection and development of a carrier state whereby the dog will be clinically asymptomatic for disease yet provide a source of contagion through the shedding of serovars in its urine. Additionally, vaccinating against these specific serovars does not afford protection against other serovars.
http://www.labbies.com/lepto.htm
For at least one type of lepto vaccine, the dog can still carry it.