Ask the Vet

Reaction to Vaccine or a Shift in the Pack Order

After a routine rabies vaccination, one reader's dog behaved more aggressively than it had in the past. Was this a reaction to the vaccine or something else? (DTN/Progressive Farmer photo by Anna Mazurek)

Question: My wife and I have five dogs of various breeds. Two of them, our Lab mix and our Pyrenees mix, received their annual rabies shots a year ago and had no reactions. Both dogs are male. This year, however, after the Pyrenees mix received his annual rabies shot, he started to attack the Lab. In the past, both have gotten along well together. These attacks have been bad enough to cause bleeding and puncture wounds. Is it possible the Pyrenees mix has had a negative reaction to the rabies shot?

Answer: My initial response is that I do not think there is a link here. That said, a Google search reveals lots of anecdotal reports of vaccines leading to aggression. I went a little further and called the company that supplies our vaccines. The veterinarian I spoke with said she has been handling vaccine-related calls for two years and has never had a case reported to her. Nor was this discussed in her training sessions.

I am not one to sweep anything under the rug, but the Internet is a very dangerous place, and the antivaccine movement is alive and well in this country (hence the measles outbreaks we have seen in humans). There is no question that vaccines have been the single most important advancement in human and animal health ever. Antibiotics do not even come close.

In the case of your dogs, this really sounds like a hierarchical issue where the younger animal may be trying to change the "pack order." The trip for vaccines, maybe a little stiffness and soreness after vaccinations, or some other change may have played a part in this change in behavior, as well.

You could ask your veterinarian to report the event to the manufacturer of the vaccine or do so yourself through the website for the USDA Animal and Plant Health Inspection Service (APHIS) at