WHAT IS HERD IMMUNITY - 356

           WHAT IS HERD  IMMUNITY 

From time to time , we come across terms which sound highly scientific and  rather   difficult to understand . There is almost a deluge of such terms during recent times  in these difficult days . PANDEMIC , EPIDEMIC, CONTAGIOUS  HYDRXYCHLOROQUIN , REMDESIVIR AND THE LATEST TO JOIN THE LIST BEING 

HERD IMMUNITY  

Being just about Passable in my English and far from being Versatile in Tamizh ,  my offhand translation to  AATTU MANTHAI PAZHAKKAM , somehow does  not seem to have a connect with the issue on hand  . 



Herd immunity seems to be the final frontier to be conquered in this fight against the pandemic . How fast we achieve this is the big question . Immunizing a sizable population is the agreed way to go about this as is being insisted  by the learned Medical Fraternity. All this makes HERD IMMUNITY sound even more interesting  . So then , what is this all important HERD IMMUNITY  ? 

Here is where , our saviour at all  such difficult times Mr Google or should it be Miss Google comes to help via their Wikipedia .


Herd immunity  

Herd immunity (also called herd effect, community immunity, population immunity, or mass immunity) is a form of indirect protection from infectious disease that can occur with some diseases when a sufficient percentage of a population has become immune to an infection, whether through vaccination or previous infections,[1] thereby reducing the likelihood of infection for individuals who lack immunity.[2][3][4] Immune individuals are unlikely to contribute to disease transmission, disrupting chains of infection, which stops or slows the spread of disease.[5] 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.[2]

The top box shows an outbreak in a community in which a few people are infected (shown in red) and the rest are healthy but unimmunized (shown in blue); the illness spreads freely through the population. The middle box shows a population where a small number have been immunized (shown in yellow); those not immunized become infected while those immunized do not. In the bottom box, a large proportion of the population have been immunized; this prevents the illness from spreading significantly, including to unimmunized people. In the first two examples, most healthy unimmunized people become infected, whereas in the bottom example only one fourth of the healthy unimmunized people become infected.

Individuals can become immune by recovering from an earlier infection or through vaccination.[5] 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.[6][7] Once the herd immunity threshold has been reached, disease gradually disappears from a population.[7] This elimination, if achieved worldwide, may result in the permanent reduction in the number of infections to zero, called eradication.[8] Herd immunity created via vaccination contributed to the eventual eradication of smallpox in 1977 and has contributed to the reduction of other diseases.[9] Herd immunity applies only to contagious disease, meaning that it is transmitted from one individual to another.[7] Tetanus, for example, is infectious but not contagious, so herd immunity does not apply.[6]

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.[10] Mass vaccination to induce herd immunity has since become common and proved successful in preventing the spread of many infectious diseases.[11] Opposition to vaccination has posed a challenge to herd immunity, allowing preventable diseases to persist in or return to populations with inadequate vaccination rates.[12][13][14]

The exact herd immunity threshold (HIT) varies depending on the basic reproduction number of the disease. An example of a disease with a high threshold is the measles, with a HIT exceeding 95%.[15]

                      

                                   

                             





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