Vaccine Doses - Why the Same for All Sizes of Pets?

Chihuahua on Great Dane's back
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This question came up on Twitter: "Why does my 5 pound Chihuahua receive the same dose of a vaccine as my 50​-pound Lab/Collie cross?"

Vaccine Doses

This question was asked after I wrote about the difference between 1 and 3-year rabies vaccinations and is a great question. Most vaccines are 1ml (milliliter) and given via a syringe subcutaneously (SQ or under the skin) or intramuscularly (IM). The most notable exception would be the nasal bordatella vaccine for kennel cough, which is administered via a soft plastic applicator tip in the nostrils.

Vaccines are given to puppies and kittens after 6 weeks of age and adult dogs and cats of all sizes. Rabies is given later, typically between 4 and 6 months of age for dogs and cats.

Why is the dosing the same for all sizes of dogs and cats?

Medications that are dosed by weight, such as antibiotics, must reach an effective level in the blood and tissue to perform their function. In this case, to fight infection. The bigger the animal, the more area to cover.

Vaccines are used to stimulate the animal's immune system, which is not something measured by weight. At least not between a small dog and a large dog. According to a source on VIN.com1, larger animals do get larger doses.

  • For reference:
  • dogs and cats - 1 ml
  • horses and cattle - 2 ml
  • elephants - 2 to 4 ml

Do smaller animals have more vaccine reactions?

Any animal can have a reaction to a vaccine. For very young or small body weight animals, it may be a good idea to spread out the vaccinations to allow the body's immune system to not be overwhelmed with mounting a response. For example, give the distemper vaccination, wait 1 to 2 weeks, then give the rabies vaccination. Note: normal puppy and kitten core vaccination schedules are usually given at 3 to 4-week intervals until 16 to 18 weeks of age. Please speak to your veterinarian for pet-specific vaccination protocols.

My breeder gave half a vaccine to my puppy because she is so small. Is this OK?

In a word, no. The protection afforded by the vaccine is now a question mark. The vaccine manufacturer will not 'guarantee' the protection level of a vaccine that has not been administered according to established guidelines.

Please see "Suggested Reading" and additional links below for more information about vaccinations and pets.

Reference: VIN.com1 is a subscription-based resource for veterinarians.

Please note: this article has been provided for informational purposes only. If your pet is showing any signs of illness, please consult a veterinarian as quickly as possible.