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Evolutionary change in pathogen populations takes place on at least 2 distinct scales. Evolutionary change in pathogen sub-populations within a host can occur (as has been well-documented in HIV), but evolutionary change in the pathogen population can also take place at the community level if some strains are more effective at being transmitted from person-to-person than others. Evolutionary biologists have long been inter- ested in such "levels of selection" and it is clearly important that these issues be incorporated into any theory that deals with the evolutionary consequences of vaccination. Under this theme, the following questions would be addressed: how do different types of vaccines and/or vaccination strategies affect evolutionary change at these two levels? Is evolutionary change at one level often expected to oppose evolutionary change at the other? For example, does vaccination tend to result in the evolution of escape mutants within vaccinated individuals, but these escape mutants are nevertheless selected against at the population level (because they do not transmit well)? If so, when might we expect there to be suffcient time for compensatory evolution to occur within an individual that allows for effi- cient transmission between hosts? Are there vaccination protocols that minimize the probability of these sorts of problems occurring? | |
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