Vaccinations are one of the most hotly debated topic in veterinarian medicine, not just by ‘natural’ websites but also by highly qualified veterinarians and immunologists which have dedicated their professional scientific careers to the topic and so actually know what they’re talking about.

So to have this discussion, I’m going to have to go over some of the basics of vaccines so we’re all on the same page. I also request that if you have something to contribute to the topic, you add it in a reply or reblog rather than submitting a separate ask, so the conversation can stay in one place. Otherwise readers get lost.

I actually attended an immunology conference in 2010, and most of its discussions was around vaccines. Over the week we attending veterinarians spent 38 hours discussing vaccines, schedules, reactions, complications and associated illnesses in depth, specialists and generalists alike. Then the last two hours were an open forum for questions which was attended by a member of the general public, who actually stood up and basically asked “What are vets doing about adverse vaccine reactions and why aren’t they doing more?”

It was very tempting to just point to the prior 38 hours that week we’d spent answering that question.

My point is that vaccines and immunology is not a quick or easy topic if you want to understand it and not just jump on a sensationalist bandwagon.

Why do all members of a species receive the same dose vaccine instead of a mg/kg dose like other drugs?

Most drugs are administered in a mg/kg manner, that is to say larger animals get a larger dose and smaller animals get a smaller dose.

This in itself isn’t even strictly true. To be most accurate, drugs should generally be calculates by a mg per surface area, but calculating surface area is a pain in the backside and so we generally only do it for drugs with an exceptionally narrow safe dose range, like chemotherapy. To make things faster, for most dogs we will use body weight to make our calculations, though some medications will have different dose rates for dogs above or below a certain size.

Vaccines and hormones don’t follow this rule. For these sorts of medications there’s not really a per bodyweight dose, just a threshold where the dose is ‘enough’. Double, triple or quadrupling a dose of oxytocin, for example, does not actually do anything once they’re reached that ‘enough’ point. Doubling a vaccine dose does not increase the protective immunity once the initial dose is ‘enough’.

This might seem counter-intuitive, especially when you look at the diversity of sizes in dogs. Surely a vaccine administered to a chihuahua will be more concentrated in its body than the same vaccine administered to a great dane? Well it probably is, but as long as we have an effective dose in both, it will still work.

What are adverse vaccine reactions and how do they relate to vaccine dose?

Vaccines actively stimulate the immune system, and like all medications in use everywhere (unlike homeopathy which is water and wishful thinking) they do things we want and things we don’t want. The things we don’t want are termed ‘adverse effects/reactions’, and they vary in their frequency and severity. They include:

fever (quiet or reduced appetite for 12-24 hours)

tenderness at injection site

anaphylaxis (swollen face and paws, like a bee sting reaction)

Immune mediated disease (eg IMHA)

Some cancers (sarcomas, specifically)

Death

But don’t panic!

Take a moment to consider the potential reactions on the list. Fever and tenderness is because the immune system is doing its thing, it’s responding (appropriately) to the vaccine. These adverse reactions are minor and often require no intervention at all, though some repeat offenders might get an antihistamine with their vaccines in the future. They are also both more likely in juvenile, small animals and so are potentially related to the dose of vaccine or adjuvant per kilogram body weight.

So if smaller animals are more likely to show tenderness and fever after a vaccine, which are indications that the body is responding, then they might still respond to a lower dose of vaccine.

More on that later.

Anaphylaxis and death are not dose or frequency dependent. They are an inappropriate response by the immune system, just like life threatening peanut allergies in humans. Because the immune response is blown so out of proportion, it doesn’t matter what the dose is, you will still get the reaction.

If a person with a peanut allergy eats a single peanut, the reaction is going to be the same as whether they ate a whole jar of peanut butter. Same with the vaccine. If it’s going to happen, it will.

This is independent of dose and completely unpredictable, but rare. Death is especially rare. Some brands of vaccine might seem more or less likely to cause anaphylactic reactions than others, but the jury is still out on this.

Immune mediated diseases and cancers are particularly interesting, and have grabbed a lot of attention from sensationalist media over the last decade. There are lots of different ones that might be associated with vaccines, but I’m going to focus on the most common two from each category because I don’t intend to lecture you for 38 hours.

Immune Mediated Haemolytic Anaemia (IMHA) Is a very interesting disease where the body attacks its own red blood cells, destroying them and causing anaemia. Some quick and dirty facts about IMHA:

33% of cases occur within 3 months of a vaccine

50% of cases also have some sort of cancer (Haemangiosarcoma (HSarc) being most common)

Approximately only 50% survive

If IMHA was completely independent of vaccination, and the dogs were all getting a vaccine once a year, you’d expect 25% of cases to occur within 3 months of a vaccine. 33% is a little suspicious. But we can’t blame vaccination for all cases of IMHA, not even close, with all those nasty HSarcs around, which on their own only have a survival rate of a few months.

In a nutshell, IMHA can be triggered by any immune system stimulation at all. For many dogs, vaccines will be the most common immune system stimulus they encounter, but cancers and viruses can do it as well. It’s not fair or accurate to blame vaccines for causing all IMHA, but we also can’t discount the possibility in an individual patient.

Injection site sarcomas (ISS) are the specific cancer associated with vaccines, especially in cats. This cancer is slow to spread but difficult to remove, and seems to be more associated with the rabies, FIV and FeLeuk vaccines more than others.

Again, however, it’s not just caused by vaccines. Any injection in a cat can trigger this type of neoplasia, and so can cat bite abscesses. It’s just that the vaccines are going to be the most common type of injection your typical cat gets.

In both IMHA and ISS, they’re basically just bad luck when they occur, but they will be independent of the dose. They’re either going to do the thing, or they wont.

So reducing the dose of a vaccine will probably not save any animal lives, but may reduce the adverse reactions that owners most frequently complain about (fever and tenderness). It might benefit the patients somewhat, but it is potentially blown a little out of proportion.

That said - I have never administered a rabies vaccine in my life. That’s a perk of living in Australia, we just don’t have it here. I don’t have boots-on-the-ground experience of that specific vaccine, so perhaps the frequency of adverse events are different to what I see with our vaccines.

Why don’t we vaccinate with lower doses ‘off-label’?

Off label is a term we use when we use a drug differently to how the manufacturer recommends, in this case using less than a single dose of vaccine for a patient.

Basically, we can’t guarantee it works.

This is especially problematic for rabies vaccination, which is done not only to protect the vaccinated animals, but also humans they might bite in the future.

If a veterinarian uses a half dose, which has unknown efficiency and may not work, to vaccinate a dog, which then goes on to bite somebody but that person does not get rabies post exposure prophylaxis because they assume the dog is fully vaccinated, that human might die. 

You just don’t know whether it worked or didn’t, whether the dog and then human are safe or not.

Risking human health in this way is generally seen to be completely unacceptable by the wider veterinarian community.

So what do I actually think?

Congratulations if you’ve read all of this and you’re still here with me. You’re doing great, well done.

Personally, I think we could potentially lower the dose (or frequency) of some vaccines, but never off label.

I would like to see more vaccine research and development for more low-dose vaccines, specifically for juvenile or tiny patients. Most vaccines would be tested in beagle-sized dogs, I would like to see a whole slew of testing done on under 5kg dogs. If we can lower the dose for these tiny ones, it might mean we need to stock two different versions of a vaccine, but we’re doing that with trivalent vaccines anyway, and I think that’s how the future will go in wealthy and developed countries.

I think the future of veterinary medicine will include more single antigen vaccines, titre testing, microdosing and changes in vaccine frequency, but I will touch on all of those in another ask (hopefully) later today because this one is long enough.