Examining Vaccines in Light of the Evolution of Virulence

Making policies about infection-control not only requires information about pathogen transmission but also information about pathogen evolution. According to Nat F. Brown et al. in their article “Crossing the Line: Selection and Evolution of Virulence Traits,” pathogens and hosts have a paradoxical relationship—pathogens damage the same host that they depend on for survival. However, Brown et al. argue that pathogens are still evolutionarily flourishing species because different strains and variations of pathogens exist. In order to successfully combat infections, public health officials, according to the authors, should see how each of these strains evolves and acquires virulence.
Although Brown et. al’s conclusion makes sense to me, I have still found some unexplained concepts in the article. The authors devote a whole section to defining the terms “pathogen” and “virulence.” Although their definitions seem sound, the authors mention that they cannot use Koch’s postulates in categorizing whether or not a species is pathogenic. However, the article neither mentions what Koch’s postulates are, nor does it give me a citation for reference. Most importantly, the article recommends that public health officials examine the evolution of virulence in pathogens but never really gives a concrete example that shows the usefulness of doing so. In order to investigate these areas of interest myself, I have come across other sources that give more information about Koch’s postulates and the evolution of virulence in pathogens. My findings describe that the ideas found in Brown et al’s article—that virulence impacts the force of a pathogen—can be applied to vaccinations and disease prevention in the sense that certain vaccines can increase or decrease virulence.  
“Crossing the Line: Selection and Evolution of Virulence Traits” defines pathogen as “an organism capable of colonizing a host organism where the interaction results in a disease.” The article then mentions Koch’s...