What characterizes a susceptible host?

A susceptible host is characterized by an inability to resist infection by microorganisms. This means that when a pathogen such as a virus, bacteria, or fungus enters the body, the host's immune system is either weak or compromised, allowing the pathogen to thrive and potentially cause illness. Various factors can contribute to a host's susceptibility, including age, pre-existing health conditions, nutritional status, and stress levels, all of which can impair the immune response.

In contrast, the other choices describe individuals with various levels of immunity or resistance. For instance, a person with a strong immune response or who can easily resist infections would not be deemed susceptible, as their body would effectively fend off pathogens. Individuals who have been vaccinated against all diseases might have a heightened level of immunity, further reducing their susceptibility to infections.