FAQ Related to Vaccination of Dogs



Puppies receive antibodies from their mother after they are born, through the colostrum (the first milk). The age at which puppies can effectively be immunized is proportional to the amount of antibody protection the young animals received from their mother. Antibodies are small disease-fighting proteins produced by certain types of cells called 'B cells.' The proteins are made in response to 'foreign' particles such as bacteria or viruses. These antibodies bind with certain proteins (antigens) on foreign particles like bacteria, to help inactivate them.

High levels of maternal antibodies present in a puppy's bloodstream will block the effectiveness of a vaccine. When the maternal antibodies drop to a low enough level in the puppy, immunization by a commercial vaccine will work.

The antibodies from the mother generally circulate in the newborn's blood for a number of weeks. The complicating factor is that there is a period of time from several days to a couple of weeks in which the maternal antibodies are too low to provide protection against the disease, but too high to allow the vaccine to work and produce immunity. This period is called the window of susceptibility. This is the time when despite being vaccinated, a puppy can still contract the disease. This window of susceptibility can vary widely. The length and timing of the window of susceptibility is different in every litter and between animals in the same litter. Let us take canine parvovirus as an example.

A study of a cross section of different puppies showed that the age at which they were able to respond to a vaccine and develop protection (become immunized) covered a wide period of time. At six weeks of age, 25% of the puppies could be immunized. At 9 weeks, 40% of the puppies were able to respond to the vaccine and were protected. The number increased to 60% by 16 weeks, and by 18 weeks, 95% of the puppies could be immunized.

Since the length and timing of the window of susceptibility varies so widely, it is impossible for us to determine when is the best time to vaccinate each individual puppy. There are just too many variables. For this reason, young animals are given a series of vaccinations in hope that we can vaccinate the animal as soon as it leaves the 'window of susceptibility.'

To provide the best response, the first time an animal is being vaccinated against a disease, repeated vaccinations are usually given 2-4 weeks after the prior vaccination. The first vaccine more-or-less primes the immune system, and the subsequent vaccination(s) increase the immune response. If a period longer than several weeks occurs between this first series of vaccinations, the immune system is no longer 'primed,' and less of an immune response will result from the subsequent vaccination. It is therefore recommended that if more than 2-3 months has occurred between vaccinations in a young animal, or the vaccination status of an animal is unknown, the animal should be given two vaccinations 2-3 weeks apart. (This does not apply to rabies vaccinations.)





The age at which the puppy received the last vaccination is the most important factor in determining boosters. To provide the best response, a puppy needs multiple vaccinations for distemper, parvovirus and hepatitis until he reaches at least 16 weeks of age. He should be given one booster again when he reaches one year of age. If his last vaccination as a puppy was before he reached 12 weeks of age, it is generally recommended that he be given a series of two boosters. The reasoning behind this: we do not know in an individual puppy how long the maternal antibody levels persist and may interfere with the puppy's response to the vaccine. In many puppies the maternal antibody is still present at 12 weeks of age so there may be inadequate response to the vaccine at that age.





There are three main reasons why a vaccinated dog would still get the disease: First, the dog's immune system may not have been functioning adequately at the time of vaccination, so a proper response was not achieved. Secondly, and much less likely, there may have been a characteristic of the vaccine that produced a suboptimal response. For instance, the strain of virus in the vaccine may have been different than the strain that caused disease in the animal. Finally, there is always the possibility of human error such as improper storage or mixing of the vaccine. When a vaccinated animal still gets the disease, some term this 'vaccine failure,' although it is more likely a failure of the immune system to respond than a problem with the vaccine itself.

Parvovirus is a serious case in point. How can a puppy get the disease and possibly die if it was vaccinated? Unfortunately, for some reason, the vaccine did not stimulate the immune system enough to protect the puppy from disease. The reason may be interfering maternal antibodies, the vaccines themselves, the dog's own immune system, or genetics. By far, the most common reason in puppies is interfering maternal antibodies.


NOTE:  The information on this page was taken from Doctors Foster and Smith.  They provided such a nice array of information that we decided to use some of their Q & A to help educate our readers.  However, we have only supplied a small portion of information here.  For more Q & A on vaccinations visit:  Doctors Foster and Smith