herd immunity

herd im·mu·ni·ty

the resistance to invasion and spread of an infectious agent in a group or community, based on the resistance to infection of a high proportion of individual members of the group; resistance is a product of the number susceptible and the probability that susceptibles will come into contact with an infected person. Synonym(s): group immunity

herd immunity

A measure of the transmission potential of a disease, which corresponds to the number of secondary infections produced by a typical case of an infection in a population that is totally susceptible, and can be quantified by counting the number of secondary cases following the introduction of an infection into a totally susceptible population.
Herd immunity occurs when a significant proportion of the population (or the herd) have been vaccinated, and this provides protection for unprotected individuals. The larger the number of people who are vaccinated in a population, the lower the likelihood that a susceptible (unvaccinated) person will come into contact with the infection. It is more difficult for diseases to spread between individuals if large numbers are already immune, and the chain of infection is broken.
The herd immunity threshold is the proportion of a population that need to be immune in order for an infectious disease to become stable in that community. If this is reached—for example due to immunisation—then each case leads to a single new case and the infection will become stable within the population, that is, R=1. If the threshold is surpassed, then R<1 and the disease will die out.
For an epidemic to occur in a susceptible population, R0 must be >1 for the number of cases to increase. If the R0 is < 1 the number of cases decreases, as occurs when a new vaccine is introduced.
This is an important measure used in infectious disease control and immunisation and eradication programmes.
Factors affecting R0
• Rate of contacts in the host population;
• Probability of infection being transmitted during contact;
• Duration of infectiousness.

herd im·mu·nity

(hĕrd i-myū'ni-tē) The resistance to invasion and spread of an infectious agent in a group or community, based on the resistance to infection of a high proportion of individual members of the group.

herd immunity

resistance of a population to a particular PATHOGEN due to IMMUNITY of a large percentage of that population to the pathogen.

单词	herd immunity
释义	DictionarySeeherd herd immunity herd immunity [′hərd i‚myü·nəd·ē] (immunology) Immunity of a sufficient number of individuals in a population such that infection of one individual will not result in an epidemic. herd immunity herd im·mu·ni·ty the resistance to invasion and spread of an infectious agent in a group or community, based on the resistance to infection of a high proportion of individual members of the group; resistance is a product of the number susceptible and the probability that susceptibles will come into contact with an infected person. Synonym(s): group immunity herd immunity A measure of the transmission potential of a disease, which corresponds to the number of secondary infections produced by a typical case of an infection in a population that is totally susceptible, and can be quantified by counting the number of secondary cases following the introduction of an infection into a totally susceptible population. Herd immunity occurs when a significant proportion of the population (or the herd) have been vaccinated, and this provides protection for unprotected individuals. The larger the number of people who are vaccinated in a population, the lower the likelihood that a susceptible (unvaccinated) person will come into contact with the infection. It is more difficult for diseases to spread between individuals if large numbers are already immune, and the chain of infection is broken. The herd immunity threshold is the proportion of a population that need to be immune in order for an infectious disease to become stable in that community. If this is reached—for example due to immunisation—then each case leads to a single new case and the infection will become stable within the population, that is, R=1. If the threshold is surpassed, then R<1 and the disease will die out. For an epidemic to occur in a susceptible population, R0 must be >1 for the number of cases to increase. If the R0 is < 1 the number of cases decreases, as occurs when a new vaccine is introduced. This is an important measure used in infectious disease control and immunisation and eradication programmes. Factors affecting R0 • Rate of contacts in the host population; • Probability of infection being transmitted during contact; • Duration of infectiousness. herd im·mu·nity (hĕrd i-myū'ni-tē) The resistance to invasion and spread of an infectious agent in a group or community, based on the resistance to infection of a high proportion of individual members of the group. herd immunity resistance of a population to a particular PATHOGEN due to IMMUNITY of a large percentage of that population to the pathogen. LegalSeeimmunity
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