What does vaccination do? Vaccines contain "antigen", which is a specific protein (or in the case of a live virus vaccine, a weakened form of a virus) which stimulates an animal's immune system to produce antibodies. These antibodies bind up and neutralize specific viruses or bacteria which enter the body, and thereby prevent or ameliorate the resulting disease. The type of immunity caused by vaccination is called "active immunity". Of course there are some animals born with defective immune systems, who cannot respond normally and develop normal amounts of antibody. This group accounts for a small but significant number of vaccination failures.

Puppies are born with some immunity from their mothers. However the main source of early protection from disease is obtained from the first milk, or colostrum. This immunity, derived from the mother, is termed "passive immunity". These antibodies decline steadily in the puppy's blood, beginning shortly after birth. But if the mother had a high antibody level, and passed a large amount of that antibody to her pups, these antibodies may persist for up to 18 weeks.

Now here is the catch! The same antibodies that bind and neutralize a virus, can also bind and neutralize a vaccine. If a vaccine is given while the puppy still has a high level of passive antibodies, the vaccine may be completely neutralized, and therefore will be ineffective in stimulating active immunity. If the shots are poorly timed with respect to the declining level of maternal antibodies, then the pup becomes vulnerable to infection.

The graph below shows two puppies. Puppy A has a high starting level of passive immunity, and Puppy B has a low level. It really dosn't matter, because both pups become susceptible at that time when their passive immunity declines below a protective level, and they have not yet developed active immunity. Puppy A is susceptible at 16 weeks, and Puppy B at 8 weeks.

Catherine Marley
Kai-La-Sha

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