Is Your Small Pet Being “Overdosed” with Vaccines?

By Dr. Grace Shook

Let’s face it, vaccines are a touchy subject these days, no matter what area of medicine you’re in. As a veterinarian who has been practicing over a decade, one of the main areas of client confusion centers around the perceived “dose” of vaccinations for our beloved pets. Owners often wonder why a puppy, kitten, or small breed of pet would receive the same volume of vaccine as a large breed of pet. Certainly a Chihuahua shouldn’t get the same volume of vaccine as a Great Dane, right? Actually, they absolutely should.

This debate over vaccine volume really began in 2014, when a veterinarian named John Robb in Connecticut was brought before the Board of Veterinary Medicine for a disciplinary hearing due to his advocation and practice of administering half volume vaccines to pets who were considered by him to be too small to receive full doses. Spoiler alert—Dr. John Robb nearly permanently lost his license to practice veterinary medicine over this, and is on probation for 25 YEARS. During his probation, he’s not allowed to administer any Rabies vaccinations to any species of animal. Additionally, he must be supervised by another licensed veterinarian at all times while he practices. The truth is, Dr. John Robb isn’t a veterinary immunologist, nor is he a vaccine researcher or developer, and had zero scientific evidence for such rash practices. He put the health and wellbeing of countless animals in his care in jeopardy, and the consequences have been severe.

So what IS the science behind the vaccine volume that should be administered, and why is it the same volume regardless of pet size? The first thing to understand is the difference between a medication and a vaccination. Medications are administered in a specific amount as determined by the body weight of the patient. The dose for a medication is based on reaching the needed concentration of the drug in the target tissues of the body, which is heavily influenced by patient body weight in most cases. Most often, the dose for a particular medication is given in milligrams (mg) of the drug per kilogram (kg) of the patient’s body weight. Therefore, as the weight of the animal changes, so will the total amount of the drug that is to be administered.

Vaccines, however, are not given in a dose wise manner like medications are. There is not a certain number of milligrams of vaccine antigen that need to be administered per kg of body weight to create the desired immune response to a vaccine. The immune system of an animal does not have a size, and functions completely independent of body weight. For example, the immune system of a Toy Poodle is not “smaller” than the immune system of a Standard Poodle, they are the same. The level of antigenic stimulation required to create a response of the immune system in a Chihuahua is therefore EXACTLY the same as the level required to stimulate the immune system of a Great Dane. Once the antigen reaches a certain threshold, the immune system is activated and stimulated to respond. This threshold is the same across normally functioning immune systems for a given species, and does not vary based on body weight. This is backed by extensive research and testing during vaccine development.

Let’s take a moment to look at how the immune system functions, and how it processes foreign pathogens, also known as antigens. There are two basic types of immunity within the body: innate immunity and adaptive immunity. Innate immunity refers to nonspecific defense mechanisms. These mechanisms include physical barriers such as skin and the lining of the intestinal tract, as well as chemicals in the blood and immune system cells that non-specifically attack any foreign cell in the body. The innate immune system does not learn to recognize specific invaders, and does not provide lasting memory of any particular antigen.

Adaptive immunity, on the other hand, is more complex, and refers to an antigen-specific immune response. Once an antigen has been recognized and processed, the adaptive immune system creates an army of immune cells specifically designed to attack that antigen. Adaptive immunity also creates a “memory” that makes future responses against a specific antigen more rapid and efficient.

Vaccinations are a targeted delivery system of a specific antigen or group of antigens, designed to stimulate the adaptive immune system. By stimulating the adaptive immune system, the vaccine creates long lasting protection against the antigen(s) contained within the vaccine. The main way a vaccine accomplishes this is by stimulating specific immune cells to produce antibodies. In order for the adaptive immune response to be activated, and for the proper cascade of events to occur that result in antibody production, there is a threshold of stimulation that must be met. To put it as simply as possible, the immune system has to be presented with enough of an antigen to recognize it as a threat, so that the adaptive immune system is activated and antibodies are produced. If this threshold is not reached, it is likely that the antibody production will be poor or nonexistent, or that the innate immune system will simply clear the antigen, and thus lasting immunity against the antigen(s) contained within the vaccine will not be produced. The volume of the vaccine given to your pet is the minimum amount of antigen required to create an adaptive immune response for that species, as established through extensive research and laboratory trials. As we’ve discussed, this antigen amount is independent of the size or weight of the animal. Giving a half or reduced volume of the vaccine will therefore result in a minimal or absent response by the adaptive immune system, and will likely leave your pet unprotected.

As you can see, it’s important that the full volume of vaccine be administered to guarantee the best possible immunity for your pet. No vaccine is 100% effective, and vaccination exceptions are occasionally made at the doctor’s discretion based on individual patient health or needs.

Hopefully this clarifies some of the confusion and diminishes some of the fear around the volume of vaccine being given to your pet. Believe me, the diseases these vaccines prevent are horrible, and as veterinarians, it breaks our hearts to see anyone witness their pet suffer through them. As your pet’s doctor, we’d much rather prevent disease than treat it. We always have your pet’s best interest at heart. So when it comes vaccination time, rest assured your little pet isn’t being given anything other than what they require to be safe and protected! Here’s to happy, healthy pets having long and full lives!

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