Herd Immunity in INDIA – Natural Immunity | Coronavirus | Blessed Mind
Herd immunity (also called herd effect, community immunity, population immunity, or social immunity) is a form of indirect protection from infectious disease that occurs when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections, thereby reducing the likelihood of infection for individuals who lack immunity.[1][2] Immune individuals are unlikely to contribute to disease transmission, disrupting chains of infection, which stops or slows the spread of disease.[3] The greater the proportion of immune individuals in a community, the smaller the probability that non-immune individuals will come into contact with an infectious individual.[1]
Individuals can become immune by recovering from an earlier infection or through vaccination.[3] Some individuals cannot become immune because of medical conditions, such as an immunodeficiency or immunosuppression, and for this group herd immunity is a crucial method of protection.[4][5] Once the herd immunity threshold has been reached, disease gradually disappears from a population.[5] This elimination, if achieved worldwide, may result in the permanent reduction in the number of infections to zero, called eradication.[6] Herd immunity created via vaccination contributed to the eventual eradication of smallpox in 1977 and has contributed to the reduction of other diseases.[7] Herd immunity applies only to contagious disease, meaning that it is transmitted from one individual to another.[5] Tetanus, for example, is infectious but not contagious, so herd immunity does not apply.[4]
Herd immunity was recognized as a naturally occurring phenomenon in the 1930s when it was observed that after a significant number of children had become immune to measles, the number of new infections temporarily decreased, including among the unvaccinated.[8] Mass vaccination to induce herd immunity has since become common and proved successful in preventing the spread of many infectious diseases.[9] Opposition to vaccination has posed a challenge to herd immunity, allowing preventable diseases to persist in or return to populations with inadequate vaccination rates.[10][11][12]
