HERD IMMUNITY refers to protection provided to a society from a disease due to large amount of immune individuals in that society.

Other names of HERD IMMUNITY

Herd immunity is also known by other names such as –
  • Herd Effect
  • Community Immunity
  • Population Immunity
  • Social immunity

HERD IMMUNITY IN SIMPLE TERMS

When a person possesses immunity to a particular disease, that person can not develop that disease even if he/she is exposed to the disease. As a result he also blocks the chain of transmission.
That particular individual is safe from the disease PLUS that individual plays role in protecting the society.
But just one individual’s immunity can not protect the whole society. Hence we need huge amount of people to be immune against a disease in order to protect the complete society all together.

How can we achieve HERD IMMUNITY against a disease?

There are only 2 ways to achieve herd immunity against a disease-
  • Infecting as many people with actual virus/bacteria (which is inhumane and disasterous)
  • Vaccinate as many people as possible (safest)
 
Vaccines are just similar to actual virus/bacteria causing diseases, just these are made to be harmless.
As a result vaccines help in forming immunity without actually making people suffer from the disease.

Which diseases can be prevented by HERD IMMUNITY?

Not all diseases can be prevented by this method. Only those diseases which fit in certain criteria can be prevented using herd immuntiy. These criteria are-

  • the disease causing bacteria/virus type should remain same
    • for example- common cold virus constantly changes its type and hence inspit of being so regular and frequent there is no herd immunity against common cold.
    • If you have immunity against type A of a disease and if that virus/ bacteria changes to type B then your immunity against type A can not fight against type B of disease.
  • contagious
    • meaning, disease transmitted from one individual to another
  • long lasting immunity
    • the immunity formed against a particular disease should stay for long enough till that disease is eliminated from the society. For example small pox and polio immunity stays in our body for life time.
Due to above criterias, there is no herd immunity against diseases like Common Cold, Tetanus, Rabies

How much population must be immune in order to achieve HERD IMMUNITY?

Well, that varries from one disease to another. Small-pox required herd immunity of >80% to get eradicated from the world.
Some experts believe that Herd Immunity against a particular virus an be considered when atleast 60%-70% of the population has effective immune response against that disease.
What is HERD IMMUNITY in simple terms? How can we attain HERD IMMUNITY?

Can we achieve 100% HERD IMMUNITY against any disease?

NO

Even if maximum efforts are given, there will always be certain part of the society which won’t take part in Herd Immunity. These people are usually those who have a compromised immune system due to some or the other reason. These include-

  • New borns
    • Children are not born with immunity against many diseases. It takes time for their immune system to develop. Also, for safety concerns some vaccines can not be given until they reach a certain age.
  • Old age people
    • Old age people have weak immune systems due to natural degeneration of their body. Vaccines might not be able to produce a proper immunity response in their bodies.
  • Steroid taking population
    • Steroids are prescribed to number of people suffering from diseases such as organ transplant recepients, auto-immune disorders etc.
  •  Cancer and AIDS patients
    • These patients have less immunity power either depending to type and location of such diseases. This is also due to the medications they are supposed to take. Cancer patients taking chemotherapy and radiotherapy also have weak immune strength.
  • Change in virus/bacteria types
    • The viruses and bacteria that affect us also evolve just like any living organism. Some, change their manner of attack, whereas some develop resistant to the immunity people have developed.
  • Patients with Spleen removed
    • Spleen plays an important role in immunity of our body. Some people have to get their Spleen removed due to reasons such as accident, complicated malaria and others. Such people have weak immunity.
  • Non Vaccine believers
    • Unfortunately, there are people who believe vaccines are just a marketing product and that they don’t need vaccines.

What is the Benefit of HERD IMMUNITY?

The group of population who can not develop a proper immune response are the ones who will get major benefit from herd immunity.
Theses are the same group of people we disused earlier-
  • New borns
  • Old age population
  • Immunocompromised individuals
  • Steroid taking population
  • Kidney failure patients
  • Liver failure patients
  • Cancer patients
Such people relay on Herd immunity for their own protection.
Other Benefits-
  • less diseases means less death
  • Also, less expense to be spent on treatment and medications
  • Some diseases leave a body disbility side effect leading to a loophole in thhe working population of the society.

Which diseases have been eliminated using HERD IMMUNITY so far?

Speaking on global basis, so far only 1 disease has been completed from the world and one more is almost on the verge of elemination-
  • Small Pox
  • Polio (eradicated in most of the world including INDIA)
 
CAN COVID-19 VIRUS DEVELOP HERD IMMUNITY?
What do your think?
Comment down your answers
 
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SOURCES-
  1. OXFORD REFERENCE https://www.oxfordreference.com/view/10.1093/oi/authority.20110803095932166#:~:text=(herd),in%20A%20Dictionary%20of%20Nursing%20%C2%BB
  2. "Herd immunity": a rough guide by Paul Fine, Ken Eames, David L Heymann
  3. OXFORD VACCINE GROUP - http://vk.ovg.ox.ac.uk/herd-immunity
  4. Herd Immunity”: A Rough Guide by Paul Fine, Ken Eames, David L. Heymann; Clinical Infectious Diseases, Volume 52, Issue 7, 1 April 2011, Pages 911–916
  5. Can infants be protected by means of maternal vaccination? by S. Esposito, S. Bosis, L. Morlacchi, E. Baggi, C. Sabatini, N. Principi
  6. Role of herd immunity in determining the effect of vaccines against sexually transmitted disease by Geoffrey P Garnett. J Infect Dis. 2005.
  7. Vaccination and herd immunity: what more do we know? by Harunor Rashid and others. Curr Opin Infect Dis. 2012 Jun.
  8. Herd Immunity: A Brief Review by M J Alam et al. Mymensingh Med J. 2016 Apr.
  9. Vaccination-Induced Herd Immunity: Successes and Challenges by Michael L. Mallory, Lisa C. Lindesmith, and Ralph S. Baric,J Allergy Clin Immunol. 2018 Jul; 142(1): 64–66.
  10. Vaccine herd effect by Tae Hyong Kim et al. Scand J Infect Dis. 2011 Sep.
  11. Introductionto Epidemiology by Ray M Merill page no 68
  12. Public Health and Epidemiology at a Glance by Margaret Somerville, K Kumaran, Rob Anderson page no 59
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