Herd immunity for COVID-19

  • IASbaba
  • October 5, 2020
  • 0
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Topic: General Studies 2,3:

  • Issues relating to development and management of Social Sector/Services relating to Health

Herd immunity for COVID-19

Context: With the COVID-19 cases increasing day by day, the theory of herd immunity has been floating around.

What is Herd Immunity?

  • Herd immunity is a form of indirect protection from infectious disease that occurs when a large percentage of a population has become immune to an infection, thereby providing a measure of protection for individuals who are not immune.
  • Initially, herd immunity, an important tool in epidemic control, was proposed as a means to overcome the pandemic. 
  • Only a certain proportion of the population needs to be infected in order to stop large outbreaks, either through naturally-acquired disease, or through vaccination. 
  • Since a vaccine is not available for COVID-19 yet, some people advocated that the infection be allowed to spread in the community until herd immunity is achieved.

Why is this being stoutly opposed?

  • The SARS-CoV-2 virus is easily transmissible and would require around 60-70% of the population to be infected to acquire herd immunity.
  • If we allow this to happen naturally, it will take a long time, of course, but more importantly, it is going to do a lot of collateral damage
  • So, even if 1 % of people who get infected are ultimately going to die, then this can add up to a huge number of people, if we look at the global population
  • Herd immunity is not a strategy or a solution by some but is considered as surrender to a preventable virus

How and when will herd immunity be achieved in this pandemic?

  • Herd immunity is achieved when one infected person in a population generates less than one secondary case on an average 
  • This corresponds to the effective reproduction number R (that is, the average number of persons infected by a case) dropping below 1 in the absence of interventions
  • With flu pandemics, herd immunity is usually attained after two to three epidemic waves, each interrupted by the typical seasonality of influenza virus, and more rarely, by interventions
  • Currently, there is insufficient confirmed information on re-infection to determine how that will influence the pandemic’s course.

What does the sero-prevalence study in India say?

  • A measure of the infection levels in the population is provided through the sero-surveys conducted by the Indian Council of Medical Research (ICMR). 
  • The second study was done between August 17 and September 22, 2020, and found the prevalence at 15.6% of the population in urban slums and at 8.2% in non-slum areas. The hotspots were not included this time.
  • In Delhi, the second round estimated a sero-prevalence of 29.1%. The study revealed that for every reported COVID-19 case, there were 26-32 infections, down from 81-130 infections per reported case in May

Are vaccines the solution?

  • Vaccines are particularly suited for creating herd immunity because their allocation can be specifically targeted to highly exposed populations, such as healthcare workers or individuals with frequent contact with customers.
  • They may have a significantly greater impact on reducing viral circulation than naturally-acquired immunity, especially if it turns out that naturally-acquired protective immunity requires boosts through re-infections.
  • With a vaccine you can achieve immunity and herd immunity safely. Through natural infection also we can achieve it at some point, but it would be at great human cost.


Until a vaccine is readied, it would be best to take actions that would slow down the progress of the virus —wearing a mask, physical distancing and following hand hygiene

Connecting the dots:

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