> It is carriers that are usefully resistent. More importantly in nature of course is that diseases and resistance to them is an arms race. Remember however that all of us are descended from forebears who survived plague.

But ...

> Disease can generate intense selection pressure on host populations, but acquired immunity in a population subject to repeated disease outbreaks can impede the evolution of genetic disease resistance by maintaining susceptible genotypes in the population. 

> This may have important implications for evolutionary population dynamics in a range of human, agricultural, and wildlife disease settings.

... acquired immunity tends to slow down the rate of
spread of disease resistance (fig. 1) and dampens the total
epizootic mortality rate during the first epizootics. However,
after the first seven outbreaks, the population with
acquired immunity suffers higher total epizootic mortality
rates (fig. 2). Thus, acquired immunity is an efficient buffer
against recurrent mass mortalities at first, but in the long
run, the maintenance of susceptible genotypes prolongs
the period with high epizootic mortality. Exactly how the
two types of immunity affect long-term extinction risk
requires further analysis ...

Harding, Karin C., B. Johan L. Hansen, and Simon J. Goodman. "Acquired immunity and stochasticity in epidemic intervals impede the evolution of host disease resistance." The American Naturalist 166.6 (2005): 722-730.

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