What You Know that Ain’t Necessarily So: Vaccination & Autoimmune Diseases

I recently gave a lecture at the Western Veterinary Conference called “What You Know that Ain’t Necessarily So.” The purpose of this was to take some common or controversial beliefs and practices in veterinary medicine and discuss the scientific evidence pertaining to these. This was not intended as a definitive, “final word” on these subjects, but as an illustration of how weak and problematic the evidence often is even behind widely held beliefs. In some cases, these practices or ideas may actually be valid, but without good quality scientific evidence, we should always be cautious and skeptical about them.

Eventually, I will post recordings of the presentations themselves, but for now I am posting a summary of each topic.

Each starts with a focused clinical question using the PICO format.

P– Patient, Problem Define clearly the patient in terms of signalment, health status, and other factors relevant to the treatment, diagnostic test, or other intervention you are considering. Also clearly and narrowly define the problem and any relevant comorbidities. This is a routine part of good clinical practice and so does not represent “extra work” when employed as part of the EBVM process.

I– Intervention Be specific about what you are considering doing, what test, drug, procedure, or other intervention you need information about.

C– Comparator What might you do instead of the intervention you are considering? Nothing is done in isolation, and the value of most of our interventions can only be measured relative to the alternatives. Always remember that educating the client, rather than selling a product or procedure, should often be considered as an alternative to any intervention you are contemplating.

O– Outcome What is the goal of doing something? What, in particular, does the client wish to accomplish. Being clear and explicit, with yourself and the client, about what you are trying to achieve (cure, extended life, improved performance, decreased discomfort, etc.) is essentially in evidence-based practice.

This is then followed by a summary of the evidence available at each of the levels in the following pyramid (which is a pragmatic reinterpretation of the classical pyramid of evidence that is a bit more useful for general practice veterinarians).

Finally, I list the Bottom Line, which is my interpretation of the evidence.

Immune-mediated Blood Disease & Vaccination

1. Clinical question

P- healthy dogs & cats

I- routine vaccinations

C- no vaccination (fewer)

O- incidence of Immune-mediated hemolytic anemia (IMHA) and immune-mediated thrombocytopenia (ITP)

1. Synthetic Veterinary Literature
   a. No systematic reviews:
   b. No CATs
2. Primary Veterinary Literature

• Case/control study
• Cases more likely to be vaccinated in previous month (26%) than controls (7%)
• Did not r/o pre-existing disease

Duval, D. (1996)

• 10% of cases vaccinated within 1 month
• No difference between cases and controls in time from vaccination to presentation

Carr, A.P. (2002)

• Proportion of dogs vaccinated within 2 months of onset not different between cases and controls
  • Cases- 16.1%
  • Controls- 44.4%

Davidow, E.B. (2004)

• Proportion of dogs vaccinated within 42 days of onset not different between cases and controls-
  • Cases- 8%
  • Controls- 14%

Huang, A.A. (2012)

• 4% vaccinated within 2 weeks
• Not primary purpose of study

Reimer, M.E. (1999)

• 2.4% vaccinated within 2 weeks
• Not primary purpose of study

Klag, A.R. (1993)

3. Human Literature
a. Systematic Reviews

• Database of 4.2 million children
• 55 cases of IMHA reported 1991-2001
• No association with vaccination

Naleway, A.L. (2009)

• ITP only associated with MMR
• 1-3 children per 100,000 doses
• This is lower than the rate of ITP caused by the diseases MMR prevents! (1:3000 to 1:6000 cases)

Cecinati, V. (2013)

Bottom Line

• 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

Reference

Carr AP, et al. Prognostic factors for mortality and thromboembolism in canine immune-mediated hemolytic anemia: A retrospective study of 72 dogs. J Vet Internal Med.2002;16:504-509.

Cecinati V. Hum Vaccin Immunother. Vaccine administration and the development of immune thrombocytopenic purpura in children. 2013 May;9(5):1158-62.

Davidow EB, et al. Risk factors for development of IMHA-A prospective case-control study. Abstract. VECCS 2004.

Duval D et al. Vaccine-associated immune-mediated hemolytic anemia in the dog. J Vet Internal Med. 1996;10:290-295.

Huang AA, et al. Idiopathic immune-mediated thrombocytopenia and recent vaccinations in dogs. JVIM 2012; 26: 142-148.

Klag AR, et al. Idiopathic immune-mediated hemolytic anemia in dogs: 42 cases (1986-1990). J Am Vet Med Assoc. 1993;202:783-788.

Naleway AL. et al. Risk of immune hemolytic anemia in children following immunization. Vaccine. 2009 Dec 9;27(52):7394-7.

Reimer ME, Troy GC, Warnick LD. Immune-mediated hemolytic anemia: 70 cases (1988-1996). J Am Anim Hosp Assoc. 1999;35:384-391