Vexed About Vaccines: Everything Pet Owners Need to Know

November 4 2020

     From the first moment your puppy enters a veterinary clinic, a conversation about vaccines is typically on the table. In fact, the first several rounds of  vaccines are often the main reason that puppies and kittens visit the vet's office. There are many reasons you should establish care early-- developing a relationship with a veterinarian for when your pet suffers from an illness or injury, acquainting your pet with the process of visiting a vet (including the unique sights, scents, and sounds) at a time when they are impressionable to socialization cues and also not under distress, as well as receiving valuable education on pet ownership, wellness, and preventative care from a healthcare provider. While anti-vaccination stances have not permeated the veterinary field quite as extensively as in human medicine, there are still many concerns and anxieties that owners face about vaccines. Like with many pet care topics, there is a wealth of misinformation floating around the web. Horror stories, blogs that denounce the practice of vaccination, and influencers that claim the whole thing is a sham abound. However, as with all things, pet owners deserve to have the facts, to have access to accurate information, so that they can make their own, truly informed decisions alongside their veterinary provider.

How Do Vaccines Work?

    When a pathogen (virus, bacteria, fungus, parasite, etc) enters your body, your immune system is activated by and begins to target something called antigen. Antigen is just a substance that your body identifies as foreign and mounts an immune response against. Antigen prompts your body to produce specific, unique antibodies, immune system molecules that will create a memory in your immune system and allow you to quickly identify and fight off that specific antigen if it is encountered in the future. This aspect of the immune system is the reason that you don't usually become ill from the same pathogen multiple times (you only have chicken pox once!), the reason that certain viruses are so effective (the flu mutates and the antigen changes, so it's able to avoid your immune system's memory), and it is the basis for vaccination

    Vaccines come in many forms. The most common are 'modified live' (also known as 'live attenuated') and 'killed' (also known as 'inactivated'). A modified live virus is a whole virus that is capable of replicating, but that has been modified from it's wild-type form to not induce clinical illness. These vaccines often produce a stronger immune response, because they more closely mirror a true infection. 'Killed' vaccines are made with a virus that has been inactivated and can no longer replicate or cause infection. The immune system won't necessarily attack this inactive virus and produce antibodies, so these vaccines are often administered with a substance to stimulate the immune response, known as an 'adjuvant.'

    In short, vaccines are designed to prime your pet's immune system to shut down a future infection swiftly if they encounter it, in a way that doesn't cause them clinical illness. Vaccines are, as such, a form of preventative healthcare. 

Are Vaccines Safe?

    Overwhelmingly, yes. As with all aspects of medicine, there are risks associated with vaccination, but those risks are relatively small and adverse reactions are rare. Because virtually all aspects of modern medicine carry some degree of risk, the decision to administer vaccines is based on an analysis that assesses potential cost against documented benefit. For example, the risk of adverse reaction associated with a parvovirus vaccination is low. The risk of that reaction being severe or life-threatening is even lower. The lifetime risk of exposure to parvovirus is high, and the risk of death or severe complication when a parvovirus infection occurs is even higher. Some dogs recover with no long-term complications, but treatment may cost hundreds, or even thousands, of dollars. That said, it's still worth discussing the most common concerns associated with vaccine administration. 

    The absolute prevalence of all forms of adverse vaccine reactions are not clear. In dogs, according the the findings of a 2005 JAVMA study that included over 1,000,000 dogs, risk of adverse reaction within 72 hours of vaccination increases with decreasing size of the dog and increasing number of vaccines administered at one time. Even in the highest risk groups, however, the risk is relatively small, with less than 1% of high-risk dogs experiencing an adverse event. Overall, the rate of adverse reactions was less than 0.5%, or less than 50 events per 10,000 dogs.  Many of these adverse reactions were mild and limited to facial swelling or hives (~50%), with systemic reactions (lethargy and loss of appetite) representing less than 10%, and collapse representing less than 1% of adverse events. A 2015 study conducted in a similar manner, but with the intent to compare rate of adverse events between vaccine types, found similar overall prevalence of adverse events. To frame this in context with risks associated with not being vaccinated, consider that unvaccinated dogs are significantly more likely to contract parvovirus, among which a 30%-90% mortality has been observed, depending on whether treatment is pursued and how aggressive that therapy is. An exam and vaccine costs around $50-$100 depending on where you live. Aggressive therapy for parvovirus can quickly amount to $1200-$3000 over the span of several days. 

    In cats, injection site sarcomas (FISS) have been associated with vaccine administration. These aggressive tumors can form secondary to injections or subcutaneous irritation/inflammation in general, though vaccines are the most common injection provided to healthy cats. This adverse event is still relatively rare. Surveys of prevalence have suggested between 1-4 per 10,000 vaccinated cats develop FISS. In response to awareness of this issue, new recommendations for feline vaccines have emerged. For example, practicioners are encouraged to vaccinate at the farthest parts of the limbs (legs or even tail), in order to faciliate more effective treatment (amputation) if a tumor forms. Additionally, guidelines have encouraged vaccinating cats as often as necessary but as infrequently as possible. Due to the additional inflammation associated with adjuvants, it is also recommended that recombinant vaccines without adjuvants be used when possible for cats. 

   There is a concern that some immune disorders, such as IMHA (immune mediated hemolytic anemia), may be linked to vaccination. While attempts have been made to investigate this further, no definitive link has been established. 

My Breeder Gave Vaccines / Can I Give Vaccines?

    The best recommendation for owners of puppies or kittens whose breeder vaccinated the litter themselves is to get boosters for those vaccines at a veterinary clinic. In that same vein, owners should not attempt to give vaccines themselves. While many vaccines are available for purchase over-the-counter, there is no guarantee that these vaccines have been transported or stored appropriately. Improper transport or storage can render vaccines ineffective. Additionally, there is always a risk of complications associated with vaccines, so it is safest for them to be administered in a medical environment. By law, rabies vaccines must be given by or under the supervision of a licensed veterinarian either way. 


    Fears regarding 'over-vaccination' are prevalent among pet owners. "Over vaccination" implies that vaccines are given either more frequently or in a greater volume than necessary to provide protection and that there are negative consequences for health associated with excess administration. While there may be some merit to the first statement, it is the latter half that lacks evidence to support it. To preface, there is nothing wrong with advocating for more research on how long vaccinations provide immunity, in order to reduce the frequency at which they need administered. However, current recommendations must be made in the context of information that is available. As discussed above, adverse reactions from vaccines are uncommon. As discussed below, the frequency of vaccines administered, and which ones are recommended, is based on data for how long immunity lasts, regional laws (rabies), and individual pet lifestyle. 

    A common concern is that a 10lb dog recieves the same volume of vaccine as a 100lb dog. This does not mean that the small dog is being overdosed or that the large dog is being underdosed. It is a reflection of the fact that vaccines target the immune response, and that response is not dose-by-weight dependent. Practicioners will often say "the dogs may be different sizes, but the immune system is the same size in all of them!" If a lower dose of a vaccine is given, in an attempt to tailor the dose to the size of the patient, there is a risk that a sufficient immune response will not occur to impart protection. In that event, a medical procedure has been performed without benefit to the patient, and that should always be avoided when possible. 

Titers as a Vaccine Alternative?

    Titers are a measurement of antibody in an individual to a specific pathogen. While titers can correlate with protection, levels must be validated to understand at what point a "positive" titer corresponds with protection and a "negative" titer corresponds with suceptibility. Titers are limited by whether or not they have been validated in the context of a specific disease, as well as by the limited scope of the immune system that they assess. There are several types of antibodies that can respond to invaders, and titers measure only one. Additionally, antibodies represented only half of the immune system-- humoral immunity. There is another arm of the immune system called cell-mediated immunity, that is not measured by titers. Only a handful of titers are validated for assessing protection in companion animals: canine and feline parvovirus (feline panleukopenia), canine distemper virus, and canine adenovirus. These are often administered through a combination vaccine (FVRCP for cats, D2APP for dogs). If owners would like to elect to monitor vaccine status through titers rather than re-vaccinate, it is a more expensive option, but it is validated. 

Additional information on titers:

To Titer or To Revaccinate (JAVMA)

Antibody Titers Vs Vaccination (Today's Veterinary Practice)

Understanding the use of antibody titers in veterinary practice (DVM 360)

Vaccine Detox

    There are some products on the market that claim to eliminate "the toxic effects of vaccines," while "preserving the protection." Any product that claims to provide benefits with no risk of negative effects should raise red flags. These products have no scientific merit behind them and are a form of predatory marketing that takes advantage of pet owner's desire to protect and care for their pets. The safety of these products is as unclear as their efficacy, and they should be avoided. 

What Vaccines Does My Pet Need?

This information is for educational purposes only and is not a substitute for veterinary care. Work with your veterinarian to discuss what vaccines are right for your pet. 

The World Small Animal Veterinary Association has a Vaccination Guideline Group that has published vaccines guidelines. These were last updated in 2016. Additionally, the American Animal Hospital Association provides guidelines for dogs (2017) and in conjunction with the American Association of Feline Practitioners, guidelines for cats (2020)

Puppies and kittens receive a series of vaccines in order to protect them when they are most vulnerable. When they're born, they are protected by 'maternal antibodies' passed down from their mother. These antibodies slowly wane as the animal ages. These antibodies also prevent the young animal's immune system from mounting an adequate protective response after vaccination. This creates a 'window of susceptibility' where maternal antibodies are too low to protect from infection, but still high enough to interfere with vaccination. It is during this window that puppies and kittens receive vaccines every few weeks. After completing that series, they 'graduate' and receive boosters one year later. At that point, the period between vaccines may be further increased, depending on the vaccine. 

Rabies, regardless of studies on the length of protection from vaccine, is mandated by local laws. It is important to stay in compliance with these laws. If your dog ever bites someone, bites another dog, is bitten by another dog, or has a scuffle with a wild rabies vector species, the outcome with animal control services, including the necessity of quarantine, the duration of quarantine, and the location where your pet is allowed to quarantine, will depend on your dog's vaccination status. Most states allow rabies to be given every 1 or 3 years, in accordance with the product label. Other states require that rabies be given every year. A number of states allow rabies exemption within certain circumstances. You can read about your local rabies laws online


* Parainfluenza is non-core, but often administered in combination with DA2P


Further Reading:

Immunology Crash Course Review

General Vaccines Information

AVMA on Vaccines

SkeptVet Articles on Vaccines

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