Is there a kind of inverse proportionality relation between a pathogen ability to infect new hosts and its ability to evade the immune defenses/medication?
The question is motivated by another one asked recently, which draws an apocaliptic scenario of SARS-CoV-2 adapting to vaccines and exterminating the mankind. My answer is that SARS-CoV-2, while being highly infectious, is not capable to such a degree of adaptation. In the same time, the examples of organisms highly adaptable to the immune defenses and/or medication, such as HIV or pathogenic bacteria, are usually less infections (at least to the extent that they cannot be transmitted through thin air). This anecdotal evidence seems to suggest that highly infectious pathogens are less capable of adaptation, whereas highly adaptable organisms are less infectious. I could justify it from the population genetics point of view: a pathogen that is both highly infectious and highly adaptable would exterminate its hosts and go extinct. This explains why such organisms do not exist, although it does not exclude an apocaliptic scenario, where such a pathogen does exterminate the mankind ;) However I would go further, claiming that there is a trade off between higher infectivity and being able to adapt to a changing environment. So I am looking for a coresponding principle in population genetics or perhaps even in ecology (e.g., a tradeoff between the replication rate and the adaptability).