Vaccination immune ineffective, but because:
A dog's own immune system is not perfect.
(2) latent or concurrent infection.
Poor health - such as the parasite is not clean, a high fever.
The injection timing was not right - mostly too early in the colostral antibody injection, part of the antigen to be offset, of course, can produce the function is significantly impaired.
5 do not follow the physician asked - more than a year has not yet appended, of course, there are still likely to be infected, because the vaccine effectiveness can only be maintained for one year.
6. Other pressing or are using certain drugs.
The injection is usually on time to prevent dog born to big problems or small problems are much lower, because the body's immune system is always in a state of alert, other pathogens are not easy to mischief.