One of the potential adverse effects of vaccination is the triggering of autoimmune diseases in susceptible individuals. There is some evidence in humans, for example, that the routine MMR vaccine (which prevents measles, mumps, and rubella) can trigger an autoimmine disease, called ITP, which destroys platelets and reduces a patient’s ability to form normal blood clots. The evidence suggests this occurs in roughly 1-3 children for every 100,000 MMR vaccinations.
While this is a real and serious risk, it is important to note that not only are the diseases prevented by this vaccine a much greater risk, but it turns out that these disease can also cause ITP and at a much higher rate than the vaccine (1 child out of every 3,000-6,000 cases). Therefore, the benefit of vaccination is clearly greater than the risk in this case.
There is, as always, far less data to determine what, if any, risk of autoimmune disease there is in vaccination of dogs and cats. Both ITP and IMHA, another autoimmune disease involving destruction of red blood cells, occur in dogs, and these have been reported to follow vaccination. However, the relevant research literature is sparse, flawed, and inconsistent. The bottom line from my previous review of the literature was this:
- Little evidence vaccination causes IMHA/ITP
- No consistent temporal association
- Data are weak
- Overwhelming majority of vaccinated animals do not develop these diseases
- Infection can be a greater risk for IMHA/ITP than vaccination
- Don’t vaccinate more than necessary
- Don’t vaccinate less than necessary
- Don’t avoid vaccination out of fear of IMHA/ITP
A small piece of additional evidence was recently presented at the American College of Veterinary Internal Medicine (ACVIM) 2017 Forum.
Moon, AKB. Veir, J. Vaccination Behavior and Adverse Events in Dogs Treated for Primary Immune-Mediated Hemolytic Anemia (Abstract HM17) ACVIM Forum, National Harbor, MD, 2017.
This study surveyed the owners and veterinarians of dogs who had been diagnosed with IMHA. Such dogs are frequently not vaccinated once they recover from the disease because of concerns that vaccination might trigger a relapse. This is often done even when there is no specific reason to think vaccination triggered the initial episode. It is a reasonable precaution, but since it is not clear that vaccination actually is a risk factor for ITP or IMHA, it is possible that these dogs are being left vulnerable to infectious diseases unnecessarily.
In this small study, survey results were available for 44 dogs. There were several relevant findings:
- The average time from most recent vaccination to the initial onset of IMHA was 351 days. Such a long period makes it unlikely that vaccination was a major trigger for IMHA in many of these dogs. It still might have been in the subset who were vaccinated closer in time to the onset of their illness. This study found no such temporal relationship, but a different study design would be necesary to confirm that.Previous studies have found only a small proportion of IMHA cases received vaccinations in the 2-4 weeks before the onset of their illness, and most found no difference in recent vaccination rates between dogs who developed these diseases and comparison dogs who did not. So far, the overall data suggests that vaccination is rarely a proximal trigger for these autoimmune disease, though whether they play a role as an overall risk factor isn’t known.
- About half of the dogs had not been vaccinated since their IMHA diagnosis. This is consistent with the common practice of many vets to eschew vaccination in dogs who have had a history of autoimmune disease. However, about half of these dogs did receive vaccines after their diagnosis, and almost all of these were rabies vaccines. This is likely because rabies vaccination is legally required in most of the U.S. and exceptions are not always allowed for dogs with a history of autoimmune disease.Only 2 of the 21 dogs who were vaccinated following their IMHA had any reported adverse reaction. These two reactions were typical of the acute hypersensitivity reaction seen with vaccination. No relapse of IMHA or other autoimmune disease was reported in the vaccinated dogs. This suggests that such dogs may not be more sensitive to vaccination than other dogs, though again the size and methodology of this study is not adequate to demonstrate that with any certainty.
- Though this is just a small bit of data, it does fit into the larger context of existing evidence in dogs, and the much more comprehensive evidence in humans, suggesting that vaccines play an extremely small role, if any, in triggering such autoimmune diseases, While caution is warranted, and certainly unnecessary vaccination should be avoided on principle, there is no justification for extreme and confident claims that vaccines are a major cause of these autoimmune diseases in our pets or that what risk may exist outweighs the benefits of appropriate vaccination.