Vaccinating cats and dogs: should you ever use less than the full dose?

Should these two canines receive different doses of vaccine based on size?

Short answer: no.

No, not even for kittens/puppies.

I've done this too, don't feel bad. There's this widespread feeling, especially among dog breeders and animal rescue folks, that splitting vaccines between young/small animals is a good thing. It saves money and seems like it would be safer somehow. The thought process goes: if a one mL dose is good for an 80lb dog, than shouldn't half or less of that amount be fine for a 10 lb dog?

But vaccines aren't drugs. You don't measure dosing by weight.

And everyone who knows what they're talking about says don't do it.

All you need to know is in the following email response from an expert to one of our board members' request for clarification:

You are correct regarding the recommendation AGAINST splitting vaccines.  This is applicable for both dog and cat vaccines.  The idea behind the recommended vaccine dose is that it contains what has been determined to be the minimum amount of antigen needed to adequately stimulate the immune system- regardless of the pet's size.  If you do not administer the vaccine properly (route, dosage), then not only can this result in vaccine failure but it also negates the manufacturer's warranty regarding the efficacy of the vaccine.  

 Regarding references: it is difficult to locate primary references since these concepts were validated in studies done some time ago.  I did find two references that might help you though - one is a recent publication, "2013 update on current vaccination strategies in puppies and kittens" by GM Davis-Wurzler (Vet Clin North Am Small Anim Pract. 2014 Mar;44(2):235-63.).  Here is the applicable quote from this publication: 

 

"The practitioner is advised to always follow the manufacturer’s directions for dose

and route of administration. Using a topical product parenterally or splitting doses

should never be done. A full dose is required to stimulate the immune system; there

is no medical basis for giving a smaller dose to a toy breed dog, and this practice could

lead to vaccine failure in that animal. If done with a rabies vaccine the practitioner is

not following federal requirements, which carries potential legal implications."

Also, WSAVA (the World Small Animal Veterinary Association) publishes vaccination guidelines for cats and dogs and under its FAQ section it states, 

"26. May I use smaller vaccine doses in small breeds to reduce the risk of adverse reactions?

No. The volume (e.g. 1.0 ml) as recommended by the manufacturer generally represents the minimum immunizing dose, therefore the total amount must be given."

(http://www.wsava.org/sites/default/files/VaccinationGuidelines2010.pdf)

I hope this helps, 

Chumkee 

Chumkee Aziz, DVM 

Resident, Koret Shelter Medicine Program

UC Davis Center for Companion Animal Health

www.sheltermedicine.com

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