Final answer:
A person with little or no immunity to a pathogen is called a susceptible host, and they can be at risk of infections such as chickenpox but may be protected by herd immunity if many others are immune.
Step-by-step explanation:
A person who has little or no immunity to infection by an organism is called a susceptible host. This means that the person does not have a specific immune response against a pathogen and is therefore at risk of developing diseases such as chickenpox if they are exposed to the virus that causes it. Individuals who are susceptible may benefit from herd immunity if enough of the population is immune to the disease, providing protection by reducing the chances of transmission.