Lately I’ve had a run on questions from veterinarians along the lines of “I have a client who is immunocompromised and their physician has said their pet should not receive a modified live vaccine. What should we do?

  • dog-nose-closeup There are a few different types of vaccines. Modified live vaccines are vaccines comprised of (as the name suggests) bacteria or viruses that have been modified to make them less virulent. They can be highly effective vaccines, as they help the immune system learn to defend the body from the normal bacterium/virus (in the same way) without having to handle the disease itself. They’re safe for normal individuals, but in immunocompromised people, these types of vaccines are typically avoided because the body still needs to “fight” the much less dangerous but still live vaccine version of the pathogen.

But what about pet vaccines?

There’s concern that giving a pet a modified live vaccine might result in a person being exposed to the same modified bacterium or virus.

But, what is the real risk?  We don’t know. However, when you think about what the issues really are, there are clearly some things to consider.

Is the “normal” bacterium/virus a problem in people?

  • If not, then the modified version won’t be a problem either. Most of the diseases we vaccinate pets against using a modified live vaccine are not caused by bacteria or viruses that can infect people, even at “full strength”. So, those vaccines are no concern at all.
  • If yes, it’s a tougher call. The main vaccine that causes concern is intranasal or oral administration of modified live Bordetella bronchiseptica, a bacterium that is one of the component causes of “kennel cough” (or more appropriately canine infectious disease respiratory complex (CIRDC)). This bacterium causes occasional infections in people. There are also a couple of reports of infections in people with the intranasal vaccine strain, but these cases either aren’t particularly strong or involve abnormal situations (such as accidentally being squirted in the eye with the vaccine).

What’s the cost-benefit?

  • If there is a potential risk, what’s the potential benefit? Does preventing disease in the animal reduce the risk to the person, because of the potential for exposure to the normal strain from the pet if it gets infected, or from the potential of being exposed to an antibiotic resistant bacterium if the animal gets sick and needs antibiotics? That’s a tough one to figure out, but certainly warrants consideration.

Is an animal vaccinated with a modified live bacterium a higher risk animal than any other animal?

  • This often doesn’t get considered. If you show me a dog vaccinated with a modified live vaccine and ask me to list the top things with which the dog is likely to infect a person, the modified live bug won’t even crack the top 10 (or 20). So, I can’t see how a dog that has been vaccinated really increases the infectious disease risk posed by a pet.

That doesn’t mean we should ignore the issue completely, since there are some things we can probably do to drop the already low risk even more. This mainly revolves around modified live Bordetella vaccination. A few simple, practical and logical measures would be:

  • Keep the high risk person out of the room when the animal is being vaccinated, to prevent high level exposure directly to the vaccine.
  • Wipe the face of the animal after vaccination to reduce the burden of the vaccine bacterium on the outside of the animal.
  • Avoid close contact with the animal’s face for a short period of time. Realistically, if someone is immunocompromised enough that they are concerned about vaccination of their dog, close contact with the dog’s face should be avoided at the best of times.
  • Encourage hand hygiene after contact with the dog. As above, that’s a good general precaution at any time, but can be emphasized during the day or two after vaccination.