But the big factor in this is all the environment that changes. If it doesn't change, then they are going to remain the same, save for small tweaks here and there.
I don't really understand what you mean by that.
Furthermore as a medical professional you really ought to be more responsible with the way you disseminate information when talking about infections diseases, particularly
herpes- at least inform people that there are multiple types of herpes (zoster, simplex, and their subtypes) and different types will tend to infect different locations, and be transmitted in different manners. Cold sores, for example, are one type of HSV, whilst the sexually-transmitted herpes is another. Best to look this up in detail if you would like to know.
Anyway, regarding the interaction between environmental, pathogenic and human factors:
Consider, for example, that the influenza virus antigenic presentation (i.e. the challenge it presents to our adaptive immune system) changes little by little for the most part, and our immune system will sooner or later latch on to these changes (maybe with some help from flu shots: evidence is sometimes equivocal on this count).
However there are two major events that dramatically influence the nature of influenza and the extent of population illness: antigenic
drift and antigenic
shift. Drift basically means change in the antigenic presentation at an increased rate, that will leave the immune system (and medicine) behind for a while, resulting in outbreaks (this happens once every 20 years or so). Shift, however, is a sudden mutation of a population that completely alters the presentation of the flu virus, leaving the population completely flat-footed and causing widespread epidemics. This happens about once every 100 years or so.
As you can see from this single example, while the fundamental principles that everything is connected to everything and therefore everything changes sooner or later, these changes can present sometimes overwhelming challenges to human survival.
So bottom line: there is no assured security in this competitive environment. There are many more factors than simply medications (you can consider this the icing on the cake even). The issue with pharmacological treatment is that anything carries risk factors, and so do drugs. Much of the advances and improvements in health outcomes is to do with social engineering and infrastructure more than anything else, which pretty much reduce prevalence of modes of infectious transmission and therefore risk factors to illness.
If you are at a place where people are always sick you might just adapt and become immune to the sickness.
This depends on the illness! Epidemiology is devoted to studying what applies to what: for example your risk of having thalassaemia is pretty much entirely tied to your ethnicity, but if you move countries while you're under 15, you will tend to inherit the risk of Multiple Sclerosis in the country you move to!
