What’s the Right “Dose” of a Vaccine for Small-Breed Dogs?

There’s a common misconception out there about vaccines that small animals should have lower “doses” of a vaccine than larger animals. This is a natural assumption stemming, most likely, from our familiarity with how medicines are dosed. However, while there are some differences in the amount of a vaccine given in different species, it is far less of a difference than would be expected if vaccines worked like drugs.

An analogy I often use to explain this is that drugs work like a dimmer switch for a lamp. You get some light with a small movement of the switch. The farther you push the switch, the brighter the light gets. There is a minimum movement below which the light stays off and a maximum above which the light won’t get any brighter. In between, however, the amount of light is proportional to the amount you move the switch. This is much like a drug, which often will have more effects the larger the dose given (though, of course, the reality is much more complicated since different drugs work in different ways, and in the real world pharmacokinetics and pharmacodynamics are highly complex and variable).

Since the dose of the drug is really the concentration in the blood or tissues, the larger an animal, the more drug has to be given to get the same amount in each milliliter of blood or each gram of body tissue. Assuming the simplest kind of drug dosing relationship, the size of the animal is directly proportional to the dose needed, meaning a dog that is 10kg will need twice as much drug as a dog that weighs 5kg. Again, reality is much more complicated, but as a basic starting point, we often dose drugs in milligrams per kilogram of body weight to reflect this kind of relationship.

However, vaccines don’t work this way. A better analogy for vaccines is a traditional light switch rather than a dimmer switch. There is a critical point at which the light goes from all off to all on. Movement below the threshold yields no light, and additional movement above the threshold gives no more light. For vaccines, there is a minimum immunizing dose (MID), a threshold at which the immune response is fully stimulated. Vaccines don’t work by being distributed throughout the body at a certain concentration, like drugs, but by triggering an essentially all-or-nothing immune response through interacting with special cells in the immune system.

The MID does vary a little by size, but not much. A horse, for example, will get complete protection form rabies after receiving only about twice as much vaccine as a dog, though the dog may be much less than half the size of the horse.

The same logic applies to any adverse effects from drugs and vaccines. In general, harmful effects get worse as the tissue or blood concentration of a drug goes up, which is very closely related to the dose given. With vaccines, adverse effects are unpredictable and not clearly related to dose. It is true that smaller dogs are more prone to allergic reactions to vaccines than larger breeds, but this likely has to do with genetic differences between breeds, not size. Smaller individuals within a breed have not been shown to be more prone to such reactions than larger individuals. The difference in size between members of the same species is almost never great enough to affect the MID, and the idea that a 10lb dog needs half the vaccine of a 50lb dog simply isn’t consistent with the biology of vaccines and the immune system.

Nevertheless, alternative medicine advocates frequently recommend smaller “doses” of vaccine for smaller dogs. There is not yet any real evidence to indicate that this would be an effective strategy to maintain immunity while reducing the risk of adverse effects. A recent “study” by Dr. Jean Dodds claims to provide some such evidence. However, this research has been supported by the American Holistic Veterinary Medical Foundation (AHVMF), and it bears many of the characteristic features of that group’s approach to research. As I’ve pointed out before, the AHVMF and associated groups and individuals seem to feel the purpose of scientific research is not to uncover the truth but to convince others of claims they already “know” are true based on personal experience or simple belief. Dr. Dodds herself has certainly shown this to be her approach before.

While Dr. Dodds’ study is only a pilot trial, and thus isn’t intended to prove anything, it is already being used as if it were evidence for giving smaller doses of vaccine to smaller dogs. The study has been published in the AHVMA journal, which is not accessible except to AHVMA members. From the information reported on her web site, it isn’t possible to evaluate completely what, if anything, we can reasonably conclude from it. But it is clear even from this limited information that the study does not provide a reason to change vaccination practices.

Thirteen dogs under 12lbs who had not been vaccinated in at least three years were enrolled in the study. Over a two-year period, antibody titers for distemper and parvovirus were taken for each dog at enrollment and then 4 months and 6 months after vaccination with a parvo/distemper vaccine. The vaccine was given as a “half dose,” though exactly what this means or how it was determined isn’t clear. The results reported were only that antibody levels went up in all of the dogs after vaccination and stayed higher than initial levels through the 6-month check.

This tells us almost nothing of relevance to the question of whether lower doses of vaccine can protect small dogs and reduce their risk of adverse events. Is the Hemopet titer a validated titer test with meaningful cutoff levels? What were the original titer levels? Were they already protective? How much did they increase, and would this make a difference between immunity and susceptibility? What vaccine history did the dogs have? Were any even susceptible to these diseases and, if so, would the vague half dose have protected them? Did any have adverse reactions? Had they had any adverse reactions to full-dose vaccination? Would they be less likely to have such reactions at the lower dose?

The unanswered questions are nearly endless, and many of them are crucial to the actual question. While a pilot trial, again, is only intended to test whether a real study is feasible and safe, the reality is that this trial is already being used to imply that giving less of a vaccine to smaller dogs is safer and just as effective as giving the intended dose. Dr. Dodds implies that on her site, and others reporting her results elsewhere do the same. Nothing about this trial justifies that claim.

Hopefully, more rigorous and transparent research will be done, but I am not optimistic. The goal is clearly to convince others of something Dr. Dodds and most of the AHVMA members already believe on faith, not to find out if this belief is actually true. As is often said about politicians, alternative medicine proponents often use science the way a drunk person uses a streetlamp: for support, not for illumination.







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21 Responses to What’s the Right “Dose” of a Vaccine for Small-Breed Dogs?

  1. L says:

    Since losing a dog to hemangiosarcoma a couple of years ago, I have had concerns about the rabies vaccine, especially for dogs under 20 pounds, and seniors (over 10).
    Also for allergy dogs that require the care of a specialist.
    I wish we knew for sure what caused these things, so that we could avoid them.
    Thanks, for the information.

  2. skeptvet says:

    Unfortunately, there is a tendency to blame vaccines and other beneficial medical interventions for any health problem we can’t specifically identify the cause for. It is natural to want to avoid bad things happening to our pets, but if we take steps that aren’t based on good science, we are as likely to harm them as protect them. There is no reason to think vaccination has ANY impact on the risk of hemangiosarcoma in dogs of any breed, so I don’t think there is any reason to suppose such a link exists or to avoid vaccines as a way of warding off this disease.

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  4. L says:

    The hemangiosarcoma thing truly broke my heart. However, I will take my other 2 in for their annuals this spring, I will try to listen with both ears.
    I was wondering what you thought of senior lab work, one of my dogs will turn 7 this month. I am thinking it is a good idea, because maybe disorders could be caught early.

  5. skeptvet says:

    I’ve written a couple of articles about doing bloodwork before surgery and screening tests generallywhich you might want to take a look at.

    The usual assumption is that checking blood tests in an apparently healthy animal is a good idea because we might find something that we can better treat if found before the dog gets sick. And sometimes this is true. However, in humans we’ve discovered that most of the time, these tests find things that either aren’t a real problem or that we can’t do anything about. And sometimes, we actually do more harm with follow-up tests and treatments than if we hadn’t one the original screening in the first place. There is a trend away from such testing in people because we’ve gotten a better understanding of the risks. Unfortunately, there isn’t any data in veterinary patients to tell us if we help or hurt more patients by doing such screening bloodwork. We definitely find things that appear abnormal, but we don’t know if finding those things helps us treat the dogs more effectively or just causes useless worry and unnecessary followup tests and treatment.

    So it’s a gamble. If anything is wrong, if there are any actual symptoms, then diagnostic testing is absolutely the right thing to do. But in a healthy pet, even an older one, it may or may not be helpful, and once in a while it can actually cause harm.

  6. Becky says:

    Does the age of the dog affect their immune response? My doctor said that next year when I am 65 I will get a stronger flu vaccine because as we age, our immune system responds less well to antigens. Is that true for dogs, too?

  7. skeptvet says:

    No one knows for sure. It is common for humans to get boosters as they age, both because immunity from earlier vaccination wanes and because their immune system isn’t as strong and the consequences of illness are greater. Yet opponents of vaccination often argue we should stop vaccinating dogs when they get older because somehow they aren’t supposed to be as susceptible to disease yet they are supposed to be more vulnerable to harm from the vaccines. It really makes no sense. Unfortunately, there isn’t much scientific research I am aware of on how immunity and susceptibility to infectious disease changes in dogs as they age, so exactly what changes, if any, should be made to vaccine protocols isn’t known.

  8. Paige says:

    The article also notes that you can glean the information you seek through Animal Wellness Magazine. Perhaps checking that first would help answer your questions above since you don’t have access to JAHVMA.

  9. skeptvet says:

    Not exactly a medical journal, but in any case I don’t see any additional information about the study there.

  10. skeptvet says:

    Dr. Dodds has added some information on her blog about the study and her conclusions.


    When challenged on the strength of evidence, she acknowledges that it is a small pilot study but also makes strong claims about the conclusions and clearly indicates no additional research was ever planned:

    “a pilot study is a small scale initial study conducted to assess outcomes and improve upon the study design, if needed, prior to performance of a full-scale research project. It is unlikely that anyone would undertake a much larger similar study, as the vaccine industry wouldn’t want it and recruiting and expecting participants to continue for 6 months is often difficult. One would need to enroll 50% more cases than needed to expect a completed case cohort of enough dogs at the end. Even with the convincing results of the current pilot study, changes in current vaccine guidelines would likely take years to implement.”

    “We had not intended to follow these dogs further, but fully expect that they will have life-long immunity to canine distemper and parvovirus as they are truly immunized and should be well-protected.”

    “Our study shows that adult small dogs could receive just a 1/ 2 dose of the boosters and be fully protected. We would recommend that serum vaccine antibody titers be measured instead.”

    She was also asked about my comments on the limitations of her study, and the response illustrates that she is beginning we unshakeable a priori conclusions and conducting the research not to test these but to simply use the results as a tool to convince others of what she already knows with certainty:

    From a reader on her blog: “Any thoughts on this (IMO being quite on the mark)?” with a link to my post

    From Dr. Dodds: “Hello ! The best thing about my colleague, Dr. McKenzie, who writes as SkeptVet, is that even his “negative” publicity or assumptions directed regularly at any holistically-minded veterinary colleague or group highlights the topic and gets readers thinking about it. After being a veterinarian myself for more than 50 years, having 27 years of NIH-funded research, and more than 150 scientific publications, high visibility inevitably brings controversy. My credentials in designing and completing this study with appropriate scientific rigor speak for themselves.

    From the reader: “So basically you’re right and he’s wrong and the real questions as to the method what signifance(if any…) can be attributed to your ‘study’ of no more than 13 dogs remain unanswered? Statistically this is a completely meaningless effort…”

    From Dr. Dodds: “As Dr. McKenzie noted, it was a pilot study. If you would like to read the full report with the statistics, then please get a copy of Animal Wellness Magazine. ”

    I do not see a publication of this study yet on the web site for that magazine. There is, however, a reference for the AHVMA journal, and if anyone has access and is willing to share the full study, I would be interested in the details.

    Dodds WJ. 2015b. Efficacy of a half-dose canine parvovirus and distemper vaccine in small adult dogs: a pilot study. J Am Hol Vet Med Assoc 41: 12-21, Winter issue.

  11. v.t. says:

    Silly question: are vaccines similar to some drugs where if you score or cut down the dose, the patient may not receive the intended effective dose? (for example, capsules or some tablets, where the active ingredient may not be evenly distributed if only part of the contents/dose are given)? Since vaccines are distributed, shipped, stored, mixed and handled in various situations, is a half-dose really complete?

    Is Dodds intending to campaign vaccine manufacturers for small doses, or, what does she plan to do with the wasted suspensions (charge the client full price?) – assuming here that each vial of vaccine (without having been reconstituted) is no longer sterile if the cap is unsealed. Seems like a lot of money for unused doses, or potentially contaminated vials (or am I overthinking this?)

  12. skeptvet says:

    Most single-dose vaccines come as a dried portion and a diluent which are mixed immediately before administration. If properly reconstituted, the antigen should be evenly suspended. Multidose vaccine vials are discouraged because antigen and adjuvant concentrations can change over time with imperfect mixing before each dose is withdrawn from the vial. And single-dose vaccines are supposed to be used rapidly (typically within an hour) after reconstitution, so storing half a dose to give another patient would not be practical.

  13. v.t. says:

    So I thought, thanks skeptvet for that.

  14. UrbanCollieChick says:

    Is the J of Holistic Vet medicine a reliable journal? Is it reputable?

    If Dr. Dodds is getting attention because of a “pilot” study, that is akin to her selling her nutriscan tests to the public for large sums of money, long before they had any peer review or official approval. I don’t know if she has any of that even now.

    Seems highly unethical to me. The AVMA won’t do anything about it though.

  15. Helen says:

    It would be helpful to know exactly what a vaccine does once it enters the body. This statement hints at it: “Vaccines don’t work by being distributed throughout the body at a certain concentration, like drugs, but by triggering an essentially all-or-nothing immune response through interacting with special cells in the immune system.” Not being a chemist or a doctor, I’d appreciate more detail on the difference between drugs and vaccines. Not analogy, but actual mechanism. If a drug only works to the extent that a certain concentration is reached, that implies (to me) that a drug gets distributed evenly throughout every tissue of the body. Which in turn implies that my big toe is capable of taking up as much flagyl as my gut does. And the more non-gut tissue I have taking up the drug, the more I have to put into the system to make sure the gut gets its share. Is that true? It also implies (to me) that the organs that are the targets of drugs all “scales” with body weight. I.e., a 100 pound dog has a thryoid gland that is 10 times more massive than a 10 pound dog’s thyroid gland. Is that really true? I’m asking because I don’t know.

    But let’s say it is true. Then for vaccines, something gets injected and I think now you’re saying that that this something does not get distributed throughout the body. But our immune cells are distributed throughout the body, so how do they all get the message if the drug doesn’t have to visit every nook and cranny that holds an immune cell? Maybe it only has to make its way to the thymus? If so, then is the thymus of a 100-pound dog 10 times the size of the thymus of a 10-pound dog? If it scales up like thyroid glands do, then we have to say yes. And so why wouldn’t you need more vaccine to impact a large thymus than you do to impact a small one? See what I mean? Light switch as analogy simply restates the claim, it doesn’t explain it.

  16. skeptvet says:

    Sorry, but you’re asking for an entire course in immunology and vaccine mechanisms as well as pharmacology, which obviously isn’t going to be possible in a blog comment section. Here are a few resources to get you started:

    How Vaccines Work (CDC)
    How Vaccines Work (NIH)
    Vaccine Types and Mechanisms Made Simple (video)
    Basics of Pharmacology (slide deck)

  17. Kathy Rosenberger says:

    I don’t have an opinion one way or the other about giving 1/2 dose vaccines to small dogs, as there isn’t enough data to support or disprove the theory. Regarding what a half dose is–I think it’s pretty well established what the standard dose is for most vaccines, so not hard to figure out what is meant by “half dose”. I do get your point about the terminology, though. Regarding the cost and waste of giving a half dose, the cost is the same to the pet owner whether a full or half dose is given. If it were determined (which I’m not saying it has been) that my dog would benefit equally from a lower dose vaccine while decreasing risks and side effects, I would gladly pay the same price and get half the dose. Hopefully a lower dose vaccine would be available eventually if this theory was proven, although with current practices in the vaccine industry, it’s unlikely that it would be much, or any less expensive.

  18. skeptvet says:

    Sure, if the evidence is developed to show a lower antigen level is equally effective and safer, I would use it too. My point is just that there is no reason to think this is true, and it is actually quite unlikely based on how vaccines work and are developed.

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  20. Dr John Robb says:

    Your wrong about the dosage information you presented. You can read the science then give me a call to discuss, thanks, Dr. Robb

    Reactions go up as the weight goes down and the Titers go up as the weight goes down when all pets are given 1cc

  21. skeptvet says:

    Rather than just making this assertion and telling me to call you, perhaps you could provide the scientific evidence that supports your claim here, for everyone to see and learn from.

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