Rabies is arguably the oldest infectious disease known to humankind, with references to it going as far back as the 24th century BCE. For four thousand years, being infected meant death, whether it was a human or another mammal. This changed in 1885, when Louis Pasteur and Emile Roux successfully tested a rabies vaccine on a human subject, who went on to live another 55 years. At the same time, the vaccine began to be used on dogs.

In 2004, the Centers for Disease Control reported there were no more cases of canine-specific rabies in the United States — only those specific to other animals, like raccoons and foxes. In the years since the rabies vaccine, many other canine vaccinations were developed, specifically designed to prevent diseases like distemper, parvovirus, canine hepatitis, parainfluenza, Bordetella (kennel cough), Lyme disease, leptospirosis, and canine influenza.

Human vs. Canine Vaccination

While statistics on the number of cases of these various canine diseases over time are hard to find, we can use human diseases as a comparison, and in every case, as vaccination rates have gone up, incidents of the diseases have gone down.

To take just one example, before a vaccine was developed, polio infected and paralyzed tens of thousands of people a year, hitting a high of nearly 60,000 victims in 1952, killing over 3,000 of them. The polio vaccine was introduced in 1955. In just over a decade, polio in the United States had almost disappeared, with the last death from it reported in 1980.

Besides polio, small pox and diphtheria have been eliminated. Measles, mumps, and rubella have declined by 99% since the days before vaccinations. But success should not make us complacent, with our dogs’ health or our own — in the winter and spring of 2015, a sudden measles outbreak in the U.S. was traced back to visitors at Disneyland and attributed to “substandard vaccination compliance” on the part of parents of the children who were affected, and who went on to infect other people.


Often referred to as “anti-vaxxers,” this is a movement that started when Andrew Wakefield reported a small study in The Lancet in 1998, claiming a connection between vaccinations and autism in children. Although the study was discredited for various reasons and Wakefield’s medical license was revoked in 2010, the anti-vaccination movement continues to this day, and a number of dog owners have taken a similar stance, refusing to vaccinate their pets.

While the list of reasons for humans not vaccinating their children is longer, with dogs there seem to be three reasons that people are leery — one is that, they claim, the vaccines contain toxic metals. The second is that vaccines can adversely affect a dog’s immune system, and the third is that dogs are vaccinated far too frequently, with many vaccines being given annually for the dog’s life.


The first claim is easy to debunk on several fronts. The most frequently cited vaccine additive, the preservative Thimerosal, strikes fear into the hearts of people because it contains mercury, which has a bad reputation of causing degenerative diseases of the nervous system.

However, the type of mercury that is highly toxic, methylmercury, is different than the type found in vaccines, which is ethylmercury. Methylmercury accumulates in the body, and it is this build-up of the metal that causes so-called “Mad Hatter’s Disease.” In contrast, ethylmercury does not accumulate in the body.

The difference is analogous to ethanol and methanol. The former is the kind of alcohol found in liquor, wine, and beer and is safe(ish) for human consumption in reasonable quantities. The latter, although a very similar molecule, is extremely dangerous. Half a teaspoon will blind a person. Less than four ounces will kill them.

The mercury compound in vaccines is not only reasonably safe for humans and animals, but it occurs in extremely small amounts and serves an important function — preventing bacteria from growing in the serum. Without an antibiotic as a preservative, the shot would literally become toxic. Although Thimerosal has been phased out of most human vaccines, it is still used in some canine vaccines. If it is a concern to you, ask your vet for a vaccine brand without it.

How Vaccination Affects a Dog’s Immune System

Regarding the second claim of vaccines adversely affecting a dog’s immune system, this can occur, but it is incredibly rare and has more to do with the dog’s genetics than anything else. For example, a condition that can cause a dog’s immune system to attack its own red blood cells has been associated with vaccination in some studies, but at a rate of one incidence in a million shots. Other studies have found no association.

Specific breeds, like Weimaraners and dachshunds, have shown autoimmune diseases in response to vaccines but, again, these are very rare, are linked to genetic defects, and would be caused by infection with the particular disease anyway.

It’s worth quoting the SkeptVet blog at length on the subject: “(I)f vaccines do precipitate such diseases, so do infectious organisms, natural substances in food, and many other possible environmental factors. These conditions are uncommon, and any risk of them posed by vaccination is undoubtedly outweighed by the protection the vaccines offer against serious infectious diseases.”

Vaccination Frequency: Core and Non-Core

The last claim of canine anti-vaxxers, that dogs are given shots far too frequently, may have some merit, but it is entirely dependent on the specific dog. Smaller dogs are more likely to exhibit allergies to vaccines, for example, and older dogs with a low risk of exposure to other dogs may not need some vaccines any longer.

It’s also important to remember that there are two classes of canine vaccination: core and non-core. Core vaccinations are for diseases that are common, easily transmitted, and severe, and in which the vaccines have been shown to be safe and effective. For dogs, core vaccinations include distemper, parvovirus, hepatitis, and rabies.

Non-core vaccines are those that protect against organisms that cause only mild diseases — the kind that usually “clear up” on their own — and which are not widespread in the area or easily transmitted from one animal to another. Non-core vaccines may also have certain known risks or are not as effective as they should be, so are only used in very specific circumstances and are not recommended for all dogs.

Talk to Your Vet

All of these are concerns that you should discuss with your veterinarian, although most veterinarians will recommend all core vaccines at regular intervals. The main reason for this is that it’s impossible to determine the level of immunity to a given disease in a dog. One may develop lifelong immunity after a single shot, while another may never develop full immunity without boosters. There’s just no test to tell the difference, so better safe than sorry.

Dr. T. J. Dunn, Jr., DVM has this to say on the subject: “I am not convinced by experience that vaccinating has a destructive effect on the overwhelming majority of animals. I am, however, convinced that vaccinating has saved uncountable lives from the ravages of parvovirus and distemper… not to mention potential rabies cases.”

All-in-all, the benefits of vaccination far outweigh the risks and, as with humans, we have all but eliminated some canine diseases — but they won’t stay eliminated unless our dogs stay vaccinated. A Pack Leader’s job is to provide protection and direction, and making sure that your dog regularly gets at least all of her core vaccinations is one of the best protections you can provide.

Author’s Addendum: Some people have contacted us mentioned “titering,” but there are misconceptions about what titer testing does, so we did not include it in the article originally. Titering will determine whether a dog has been vaccinated for a particular illness, but cannot determine the actual level of immunity that a dog has. The main use for titer testing is when taking a dog from one country to another, to verify that the dog has been vaccinated. For an in-depth discussion of the subject, check out this article by Dr. Patty Khuly VMD discussing whether titer testing is a valid alternative to vaccination.

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