How Vaccines Work

by T. J. Dunn Jr., DVM

BowTie, Inc., publisher of Dog World, grants permission to re-publish this article.
Text copyright (c) 2006 by BowTie, Inc.

The vaccine topic is a hot one, as well it should be. Few aspects of veterinary medicine evoke such strong opinions among clients and practitioners. Immunology is a complex science, and can be a challenging subject to grasp. Most dog owners understand that any dog could potentially have an adverse reaction to any vaccine. They've read about "over-vaccinating" dogs, and have heard various opinions relating to purportedly vaccine-induced illnesses. Nevertheless, millions continue to take advantage of the powerful science combating truly devastating diseases. The sometimes elusive and mysterious facts of immunology are rapidly being better understood, more refined, and better utilized to improve disease prevention.

Have you wondered what, exactly, is in that inoculation syringe? Do you have questions regarding safety, efficacy and frequency of administration? It's a good idea to ask any and all questions, because the more we know about proper health care, the better stewards we become.

Unlike drugs, the efficacious dose for vaccines doesn't vary with the size of the dog. To be effective, each dose must contain enough antigen to trigger the dog's own immune system.

I recall a client who owned an unusual pair of fawn-colored dogs - a Chihuahua and a Great Dane. She asked me a very good question one day. The two dogs were great pals (the Chihuahua being the dominant of the two), and came into the exam room together for their rabies vaccinations. I examined Thunder the Great Dane first, and administered the vaccine. After the physical exam on Chico the Chihuahua, I was just about to inject the vaccine when the owner interrupted. "Wait! You aren't going to give him the same amount that you gave Thunder, are you?" she asked with alarm.
I spent a few minutes answering her very appropriate question regarding the volume (1 milliliter) of vaccine being given to both a 160-pound dog and a four-pound dog. With some substances, such as antibiotics, the appropriate dose is proportional to body mass. With vaccines, though, decades of research show that for each vaccine there is a minimum amount of antigen particles needed to be in contact with the dog's tissues in order to stimulate appropriate immune responses, and to build immunity. Different dogs require different amounts of antigen, so vaccines are designed to stimulate a response in the highest percentage of dogs. So the critical issue is giving enough antigen to trigger a strong level of immunity. If more than the minimum amount of vaccine is administered to a dog, there's no "overdose" effect, as would occur with a drug.

In a phone conversation with Mike LaRosh, DVM, Director of Companion Animal Professional Services for Fort Dodge Animal Health, I asked about the subject of administering "too much" vaccine to a small dog. LaRosh answered, "When drugs such as antibiotics are administered to, a dog, the dose depends on reaching a certain concentration of the drug's active ingredient in the animal's body. For this reason, a larger dog needs to receive a greater dose to achieve an optimal drug level in the appropriate body tissue. Vaccines themselves do not protect dogs. Vaccines work by stimulating the dog's own immune system to develop a protective response. If this stimulus does not take place, the vaccine offers no protection even though it is in the dog's body. The stimulus caused by the vaccine must be above a threshold where the virus or bacteria is recognized as a foreign invader in the dog's body. The amount of stimulus each dog requires varies, but is not determined by size." Had my client not asked her question, she might always have wondered if Chico got "too much" vaccine.

It's common, too, for dog owners to wonder what is actually in that solution that is injected into the dog. Fort Dodge states that "the main ingredient in vaccines is the antigen, a harmless derivative of the disease organism (bacteria or virus) in a form that triggers a protective response without causing the disease. Other ingredients such as preservatives and buffers are included. Occasionally, other immune stimulators are added to help improve the protective response."

Safety and effectiveness of vaccines are always a priority before any vaccine can be produced and sold to the veterinary market. Because veterinarians are entrusted to provide health-care advice, the safeguards enacted and enforced regarding animal vaccines bolster our confidence as practitioners; we know that strict regulations are in place regulating the manufacture and sale of vaccines for dogs. The United States Department of Agriculture's Center for Veterinary Biologics (CVB) regulates veterinary biologics (vaccines, bacterins, antisera, diagnostic kits, and other products of biological origin) to ensure vaccines are pure, safe, potent, and effective. The CVB develops appropriate standards and procedures for all aspects of a vaccine's development, licensing, and production. Additionally, CVB monitors a vaccine's performance once it becomes commercially available. This is called postmarketing surveillance.

There are only a handful of manufacturers that meet federal regulations regarding interstate shipment of licensed vaccines. Major companies that have the resources for research and development of vaccines for dogs are Fort Dodge Animal Health, Merial, Pfizer Animal Health, Intervet Inc., and Schering-Plough Animal Health. There are a few small vaccine manufacturers that do not meet federal regulations and cannot ship vaccines out of the state in which they are manufactured. According to veterinarian Zack Mills, Executive Director for Veterinary Services at Merial, their
company is continually involved in advanced research to improve existing vaccine technology. For example, transdermal inoculations, where compressed air, not a needle, is used to deliver a small volume of vaccine through the skin, are already a reality in cats and are currently being evaluated for their use in dogs and puppies. This methodology may actually stimulate greater immunity, and promises to lessen the incidence of local reactions.

Mills relates that Merial is deeply involved with recombinant gene technology in an effort to improve vaccine specificity, purity and efficacy. Vaccines utilizing recombinant gene technology have an advantage their purity and lack of extraneous protein can greatly lessen the chance that an adverse reaction will occur. Using DNA sequences that code for specific proteins on the virus or bacteria, scientists assemble a vaccine that triggers the dog's immune system to create a broad immune response to only these specific, protective proteins. This spares the dog from receiving potential immune-triggering elements that are unnecessary and unwanted. (There is evidence that some of today's very effective modified live vaccines may actually suppress a dog's immune competence for a short time post-vaccination.)

Vaccinations will always be a cornerstone of health care for dogs because they confer immunity to dangerous bacterial arid viral pathogens. It's not a perfect system, though. If we keep asking questions and pushing for continued improvements in vaccine safety and efficacy, the day may soon arrive when we can all agree that vaccines are truly necessary, effective, and safe for all dogs. And maybe dogs such as Thunder and Chico will only have to have two or three transdermal air-puffs of DNA during the course of their entire lifetimes to be well protected against a wide variety of organisms. What more good news is on the horizon? Vaccines to treat cancer and other medical problems are already on the drawing board!

T J. Dunn Jr., DVM, practices in Wisconsin and manages ThePetCenter.com. Send questions to Dr Dunn atthedoctorisin©bowtioinccom.