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Herd Immunity
About Herd Immunity
Herd immunity, also called community immunity, occurs when a sufficient proportion of a population is immune to an infectious disease, preventing sustained transmission. The term came into scientific use in the 1920s. The herd immunity threshold equals 1 minus 1 divided by R0. For measles R0 of 12 to 18, the threshold is 92 to 94 percent. For polio R0 of 5 to 7, the threshold is 80 to 86 percent. For COVID 19 original R0 of 2 to 3, the threshold was approximately 50 to 67 percent. However, Omicron with R0 of 8 to 10 requires approximately 87 to 90 percent. Achieving herd immunity through infection without vaccination causes enormous mortality and morbidity. The Great Barrington Declaration in 2020 proposed achieving herd immunity through natural infection, a position criticised by many public health experts. Herd immunity through vaccination is the foundation of disease elimination and eradication.
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