What is considered herd immunity?

Herd immunity occurs when a significant portion of a population becomes immune to a disease, either through vaccination or previous infections. This immunity reduces the overall amount of the pathogen's spread within the community, providing a level of protection for individuals who are not immune, such as those who cannot be vaccinated due to medical reasons. By limiting the spread of the disease, herd immunity helps to protect vulnerable populations, lowering the risk of outbreaks and ensuring that those who are susceptible have a lesser chance of encountering the disease.

While the option that states all individuals are vaccinated might suggest a high level of immunity, it is not necessary for every single person in a population to be immune for herd immunity to be effective. Additionally, disease eradication refers to the complete elimination of the disease, which is not the same as herd immunity, where the disease can still exist but is less likely to spread due to higher immunity levels. The perception that mild symptoms equate to immunity also diverges from the concept, as herd immunity focuses on reducing the transmission of the pathogen itself rather than the severity of symptoms experienced by individuals.