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SEROLOGICAL SURVEY AND WHAT IS HERD IMMUNITY?

Focus: GS-III Science and Technology

Introduction

  • Results of a recent serological survey in Delhi are being interpreted to suggest that more than 45 lakh people in Delhi could so far have been infected (while the official confirmed cases are only around 1.25 Lakh cases) with the novel coronavirus, and that “herd immunity” could be approaching.
  • However, any talk of “herd immunity” at this stage is not only premature but also misplaced.

What was the serological survey about?

  • The serological survey was meant to detect whether the person being tested had developed antibodies against the coronavirus.
  • Since it is not possible to test everyone, detecting antibodies in random sets of people is an indirect way of estimating the extent of disease spread in a community.
  • The antibodies are proteins produced by the immune system to fight external organisms like viruses that try to enter the body.
  • These are produced only after the infection has happened, and are specific to the attacking virus or bacterium.
  • The presence of antibodies, therefore, is an indication that an infection by that particular virus or bacterium has already occurred.
  • Subsequent attempts to infect the body can be thwarted by these antibodies.

What about Vaccines then?

  • Vaccines work in a similar manner – wherein they inject harmless doses of a virus or a bacterium inside the human body to trigger the production of antibodies by the immune system.
  • These antibodies can then fight off an actual attack by those viruses or bacteria.

Do antibodies ensure Immunity?

  • The mere presence of antibodies does not mean that the person is protected against the disease.
  • What is also important is the amount of antibodies present, and whether it also includes what are known as “neutralising antibodies” which actually fight the disease.

What is Herd Immunity?

  • Herd immunity is a stage of an epidemic in which some members of a population group remain protected from infection because a majority of those around them have already developed immunity, either through vaccination or because they have been infected earlier.
  • Once a certain proportion of population gets infected, and thus builds immunity against the disease, the epidemic begins to slow down and eventually stop.
  • No one clearly knows what percentage of the population needs to be infected before herd immunity kicks in. It is different for different diseases, and different population groups.

-Source: Indian Express

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September 2022
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