Vaccine Failures
 
Vaccines are given to protect but often fails in some puppies, dogs, cats and even people.

Tests for viruses and diseases can give false positive results.
Many times a puppy/dog will test positive for a disease
(especially for in-house vet test kits) that the puppy/dog
has been vaccinated for, but hasn't actually have.

Confusing isn't it?

Let's say a young dog or puppy goes into a vet clinic with
diarrhea (especially if there's blood in the diarrhea), vomiting,
loss of appetite and generally sick, will be tested for parvo virus.
The puppy could have any number of diseases but it is not yet
sure if it is parvo.  The test will consist of taking a swab of feces
from the puppy's bottom and it is then run through a test kit to
see if it contains parvo antigens (proteins or sugars on the
surface of the virus that are specific to parvo  viruses).

If the test comes out positive, it is said that the pup has parvo.
Right?
Sometimes or maybe. 
False positives:  If a pup has been vaccinated with a live
parvo vaccine 4-14 days before the parvo test was run, the
puppy/dog will shed the vaccine -associated parvovirus antigens
into its feces and these will show a positive result
on the feces test.

Therefore, a puppy/dog that has been vaccinated and protected
against parvo will appear to have been
infected with the disease.

In general, keep in mind that if one pup in a litter has been infected with the parvo virus, (while they were still together) the entire litter would be infected also as
parvo is highly contagious.

For more information or to verify this information
check out the links below:

www.pet-informed-veterinary-advice-online.com/vaccination-failure.html

www.peteducation.com/article.cfm?c=2+2115&aid=966