The immune system of the dog is designed to produce antibodies, a type of protein, to disease agents (such as bacteria, viruses, protozoa, fungi, etc). These antibodies protect the body from infection and disease by binding to the disease agent and marking it for destruction by other parts of the immune system like killer cells, phagocytic cells, and the complement system. Thus, antibodies are the body's protection against disease.
When do antibodies form? Antibodies form ONLY after an initial exposure to a disease agent. During this initial exposure the dog has no protection from the disease agent, and, therefore, the disease must run its course. In addition, antibodies are very specific -- antibodies to a specific virus like the rabies virus do not protect the dog from any other disease agent. Thus, a dog must experience each disease before it will become protected against that disease. For some diseases this is not significant because the disease is mild and has little effect upon the dog. Other diseases, however, are more significant and can lead to serious sickness and even death.
This is how Mother Nature has designed the immune system to work. The drawback to her plan is that the dog has to survive the initial disease exposure in order to develop protective antibodies, ie become immune, to the disease. As mentioned earlier with many diseases this is not a significant problem because they are mild and cause little lasting effects. There are, however, life-threatening diseases that the dog may not survive the initial exposure to. Human ingenuity came along and said what if we could expose dogs to the disease agents of these serious illnesses in such as way as to allow them to develop protective antibodies but not develop disease. And so the vaccine was invented. All a vaccine is is an altered form of a disease agent that can be given to a dog (or other species in general) in order to stimulate the dog's immune system to produce protective antibodies without the concurrent development of disease.
With the introduction of vaccines, many devestating canine diseases like Rabies, Canine Distemper, Infectious Canine Hepatitis, and Parvo were rapidly reduced in incidence and canine mortality rates plummeted. We today do not fully appreciate the impact that these diseases had on canine populations pre-vaccination and can be without the puppyhood vaccine regime. An unvaccinated dog has absolutely NO protection against any of these disease. Do not be fooled into thinking that these diseases have been eradicated and are no longer a signifcant health threat. These diseases are still maintained at significant levels in wildlife resevoir hosts (raccoons, foxes, coyotes) and in feral dog populations. And as more people choose to never vaccinate their dogs these diseases will begin to increase among the domestic dog population as well. Thus, the risk of disease exposure is present and is present at a very significant level. Vaccination is our way of using Mother Nature's brilliant system of disease protection to maximum benefit -- protection without the need for initial disease.
Puppies like all young mammals receive antibodies from their mother to passively protect them from disease until they are old enough for their immune systems to produce their own antibodies. They receive these antibodies during the first 24-36 hours of life in the first milk, or colostrum. As an aside, this antibody transfer is why it is so important that puppies nurse as much as possible during the first day of life. How long these antibodies last is highly individual and varies considerably even among littermates. The duration of maternal antibodies is a function of how much colostrum they received, how concentrated the antibodies were in the colostrum (ie, how high the mother's antibody levels were), how fast the puppy's metabolism breaks down the antibodies (like any protein they are degraded over time), and the amount of exposure that the puppy has to disease agents. Herein lies the difficulty of vaccinating a puppy. If the maternal antibodies are at too high of a level then the vaccine will incite no response on the part of the puppy's immune system. But if the maternal antibodies drop too low then puppy is at risk for developing disease. When the maternal anitbodies are high enough to protect from disease but low enough to allow the vaccine to incite a response from the puppy's immune system is the window of optimum vaccination.
When does this window happen? Anywhere from 3 weeks to 24 weeks with average being 6 to 15 weeks and at different times for different diseases. Therefore, we are left with two options: (1) wait until puppy is 6 months old to vaccinate and leave puppy at great risk for developing life-threatening illness like Distemper or Parvo or (2) vaccinate puppies at regular intervals beginning at 6 to 9 weeks so that we "catch" the puppy during its window while at the same time minimizing the time that the puppy is at risk for developing disease. The latter option maximizes protection while minimizing risk and is, consequentially, the safest and most appropriate method of vaccinating puppies. This is the rationale behind the need for repeated puppy vaccinations beginning at 6 to 9 weeks and continuing every 3 weeks until the puppy is 4 to 6 months old.
It is absolutely critical to vaccinate puppies if we expect to continue to see reduced incidence of fatal canine diseases like Distemper and Infectious Canine Hepatitis. Parvo already claims thousands of puppies a year and will claim thousands more if puppies are not vaccinated properly. These diseases are out there and an unvaccinated puppy has absolutely NO protection from them; failure to vaccinate a puppy puts it in alot of unecessary danger. Once puppy vaccinations have produced antibodies to disease agents, frequency of vaccine boosters is something to be discussed with your veterinarian. Ample scientific data suggests that current canine vaccines confer protection in most dogs for 2 years. Whether you opt to vaccinate yearly, every other year, or check antibody levels via titers and only vaccinate as needed is a matter of personal preference. Regardless of your decision regarding vaccination of adult dogs, every puppy needs to be vaccinated and every adult dog needs an annual physical exam to detect any health problem as early as possible. And also be sure to consult local law before deciding upon frequency of Rabies vaccination most places allow 3 year vaccines but some high risk areas have counties that require yearly Rabies vaccine still.
Some things to note:
FINALLY LET ME REITERATE THAT YOUR PUPPY WILL BE EXPOSED TO DISEASE NO MATTER HOW CAREFULLY YOU SECLUDE IT. THE QUESTION IS WILL IT ALREADY BE PROTECTED VIA VACCINATION OR WILL IT BE SUSCEPTIBLE TO DEVELOPING LIFE-THREATENING DISEASE BECAUSE OF YOUR CHOICE NOT TO VACCINATE???
