the general state of immunity occurring when a sufficient proportion of a population has been vaccinated or is naturally resistant so that the proportion of susceptible individuals is too small for the disease to spread
state in which a large proportion of a population is able to repel an infectious disease, thereby limiting the extent to which the disease can spread from person to person
Good to know
The percentage of the population that must be immune to produce herd immunity differs for each infectious disease. A disease that is highly contagious, such as measles, requires a higher proportion of immune persons to achieve herd immunity than a disease that is less contagious, such as tuberculosis.
Karjaimmuunsus tekib, kui 60–80% elanikkonnast on vaktsineeritud või põdenud läbi haiguse, teisisõnu, valdav osa inimestest on muutunud viiruse suhtes immuunseks.
Karjaimmuunsus, mis tekib kas juhul kui suur hulk elanikkonnast on viirusega kokku puutunud või vaktsineerimise tagajärjel, on hästi tuntud infektsioonhaigustest lahti saamise võimalus.
Kui populatsioonis on nii palju haigustekitajale immuunseid inimesi, et see takistab haiguse levikut, öeldakse, et populatsioon on omandanud kollektiivse immuunsuse ehk nn karjaimmuunsuse (herd immunity). Kollektiivset immuunsust saab tekitada ka kunstlikult, ilma et haigust läbi põetaks. Vaktsineerimine ongi tänapäeval nakkushaiguste epideemiate ohjeldamise viis.
Herd immunity is reached when the majority of a given population -- 70 to 90% -- becomes immune to an infectious disease, either because they have become infected and recovered, or through vaccination. When that happens, the disease is less likely to spread to people who aren't immune, because there just aren't enough infectious carriers to reach them.
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