Midwestern grow-finish swine are commonly vaccinated for endemic diseases such as porcine circovirus type 2 (PCV2), Mycoplasma hyopneumonia (M. hyo) and Lawsonia intracellularis (ileitis). Vaccinations are not expected to eliminate infections from the herd, but are expected to decrease the severity of clinical disease and associated performance losses.
Our expectations for vaccine efficacy vary by the specific disease and personal experiences.
Consequently, producers or veterinarians occasionally get the sense that a "vaccine is not working" for a particular disease. Does that mean it is a "vaccine failure"? … Or is it a "vaccination failure"?
"Vaccine failure" implies the actual vaccine itself is somehow deficient and unable to stimulate protective immunity. Failures can be because the vaccine is poorly designed or lacks in potency or manufacturing quality. But more likely it is because of strain variations and lack of cross-protection. Examples of variation in efficacy could be vaccines for Streptococcus suis or swine influenza virus.
On the other hand, "vaccination failure" occurs when vaccines are improperly applied or administered. Factors that contribute to reduced efficacy in this case are numerous, often because of human errors of application or judgment. Examples include:
- Timing of vaccination is done for convenience rather than maximum efficacy.
- Ignoring the impact of maternal interference; this can change over time
- Using reduced dose (particularly a risk with killed vaccines)
- Using one dose when two are recommended
- Improper method of vaccination and site of vaccine administration (and some get “missed”)
- Vaccine handling (outdated, poor storage, no refrigeration, poor handling)
- Noncompliance in vaccine administration in not following the label (or even doing the task)
- The health (disease) of animals being vaccinated – In populations of thousands, it is hard to imagine that all pigs are simultaneously immunocompetent. There would be even larger variation in immunocompetence when vaccinating animals that are compromised by diseases (infectious, metabolic or nutritional) or stresses present at the time of vaccination.
- Conclusions based on misuse of diagnostic tests, inappropriate samples, or inappropriate interpretation of highly sensitive diagnostic tests (PCR) – Conclusions based on the use of “surveillance samples” (oral fluids, feces) do not definitively differentiate between infection and disease. Simply put, the detection of an endemic agent is not the same as the diagnosis of a disease caused by that agent.
Full text:
National Hog Farmer, December 2, 2013
By Kent Schwartz, DVM, Iowa State University Veterinary Diagnostic Laboratory