Herd protection: How does it work?

Vaccination is considered to be one of the greatest discoveries in science which has saved millions of lives and changed the course of world history. Many diseases which used to be fatal in the days of yore have become extinct or have been restricted to small pockets in the world because of vaccination. Vaccination has ensured that our children grow up in a healthier world. However, there are some children who cannot be provided with the benefits of vaccination; like very young infants or those undergoing chemotherapy for cancer. How do we give them protection from common infections? In these situations, a factor called as herd immunity comes into play.

Herd immunity is a form of indirect protection from infections that occurs when majority of a population has become immune to an infection, thereby providing protection to individuals who are not immune. 1 This can be induced by mass vaccination. To put it in simpler terms, when most children in a particular region are vaccinated, the few who are not vaccinated also get some amount of protection from that infection.

What happens when your child gets fever? You keep him home from school and play. You do this for two reasons; first to give him time to recover and secondly to prevent the infection from spreading to other children. This means that you think it is your duty to protect others from falling sick. Herd immunity follows a similar kind of logic.

How does herd immunity occur?

Some infections are contagious which means they spread from person to person. If most children are vaccinated and resistant to the germs, then the germs are less likely to spread. So the chances that the germs will come in contact with a child or a person who is not vaccinated are less. Those even the child or person who is not vaccinated is indirectly protected from the infection.

What are the benefits of herd immunity?

Once a certain threshold has been reached, herd immunity may slowly and steadily limit a disease and gradually eliminate it altogether from a population. This elimination, if achieved globally, may lead to the total abolition of that particular infection. This is called eradication. The herd immunity has had a major impact in the eradication of smallpox, has reduced transmission of pertussis, and protects against influenza and pneumococcal disease.2

 Why is herd immunity through vaccination vital?

Herd immunity can confer armour of protection to persons who cannot get vaccinated like very young infants and those with cancer and other diseases that compromise their immunity. Moreover, when vaccination levels drop below thresholds necessary to maintain herd immunity, outbreaks of infectious diseases are seen to occur.3

Hence, vaccination is not only the parents’ responsibility towards their own children, but also their public duty so that herd immunity can be accomplished for this vulnerable population and the spread of infections can be checked.

To summarize, vaccinations are the silver bullets in our medical arsenal and immunization to ensure herd immunity means protecting others while protecting yourself through vaccinations.



  1. Clin Infect Dis. 2011 Apr 1;52(7):911-6
  2. Scand J Infect Dis. 2011 Sep; 43(9): 683–689.
  3. Hum Vaccin Immunother. 2013 Aug 1; 9(8): 1815–1818.

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