So, how can a vaccinated puppy die due to parvovirus? This can be a complex situation, with many possible causes that can be difficult to pinpoint.

First, lets review a little bit about vaccination. Vaccination involves exposing an animal to a specific "harmless" agent in an attempt to stimulate an immune response by the animal. This desired immune response then tries to protect the animal from specific infectious bacterial and viral diseases. This protection can and does pass through the colostrum/milk (in the form of maternal antibodies) to help protect nursing puppies. Unfortunately, the maternal antibodies can also limit the puppies' own ability to respond to vaccination ("high titer" vaccines are becoming more successful in overriding this interference). The puppy also must gradually develop, with maturity, the ability to fully respond to vaccination - thus the need for booster vaccinations. All these factors create an unavoidable situation where the puppy has minimal protection for a short period of time - from the time that maternal antibodies are declining (due to weaning), untill the time that the puppy can adequately respond to vaccination on its' own.

Now, back to the causes of vaccination failures. The causes can be put into three main categories: host (dog) related, vaccine related, or human error related.

Host factors that can cause vaccination failure include: a deficient immune system (this can be inherited, congenital, or acquired), maternal antibody interference (as discussed above), age (very young or very old), stress, illness, fever, hypothermia, malnutrition, hormone fluctuations, already incubating disease at the time of vaccination, and concurrent therapy with certain drugs.

Vaccine related factors can include: improper manufacture and handling (always use reputable brands), improper storage/refrigeration (always purchase from reputable sources), contaminated needles or syringes (this includes cleaning with disinfectants that can destroy the vaccine), vaccine ineffective against a different/new strain of virus, overwhelming exposure, inferior vaccine (a high-titer, low-passage parvovirus vaccine is required for puppies), and the fact that vaccines are simply unable to protect 100% of the population.

Human error can cause vaccination failures due to: improper mixing of products, animal already exposed to disease at time of vaccination, improper frequency of administration, incorrect route of administration, re-using contaminated syringe/needle, and omitting booster vaccinations.

Vaccination failures are devestating and have many causes. Strict adherence to proper vaccination protocols and consideration fo the above factors should help to miminze and explain losses.