Evidence indicates that reduced general immunity within a population, whether resulting from a lack of prior exposure or waning protection, directly contributes to a higher susceptibility and greater severity of infectious disease outbreaks.
The retrieved literature contains strong epidemiological and modeling studies showing that reduced population-level immunity (due to waning, lack of exposure, or absence of vaccination) increases vulnerability to disease resurgence and more severe outbreaks. Papers [1] and [6] directly support this claim, while no papers refute it.