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How can host characteristics such as age and immunity affect disease risk?

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Know the investigations of researchers using genomic information to reconstruct the cause and transmission routes of the bubonic plague and the Black Death — epidemiology Researchers using genomic information to trace the transmission routes in past epidemics of plague.

In epidemiology, host characteristics such as age and immunity are fundamental determinants of disease risk and population-level health outcomes.12

Immunity and Herd Immunity

Immunity represents the host's resistance to a pathogen. An individual's susceptibility to infection is influenced by their innate resistance and prior exposure to the infectious agent. At the population level, the prevalence of immunity—known as herd immunity—dictates the spread of disease. When a large proportion of a population is immune, the probability of an infectious agent successfully transferring to a susceptible host decreases, effectively halting the growth of an epidemic. Conversely, populations become susceptible again as immunity wanes, individuals die, or new susceptible individuals are born.12

The Role of Age

Age significantly affects an individual's vulnerability to disease and their physiological capacity to recover.3
* Physiological Decline: As humans age, organ systems (such as the heart, lungs, and kidneys) experience a gradual decline in function and reserve capacity. This makes the elderly more susceptible to severe outcomes from infections that a younger person might recover from quickly.3
* Recovery Rates: Older individuals often require more time to reestablish physiological homeostasis following metabolic or environmental stress compared to younger individuals.4
* Exposure Patterns: Age also influences disease risk through social behavior; for example, children in crowded urban environments may be exposed to certain childhood diseases at an earlier age than those in rural settings.2