What makes Herd Immunity special and why the buzz around it rose to the top during this COVID Pandemic?

Top in Trends: Herd Immunity

The only positive change that the COVID pandemic has brought along is that it stressed on how important the adaptability of humans is, to survive anything. It made possible many things which earlier were thought impossible to do remotely. It has brought in new social distancing rules to the human race who are inherently social animals, along with the revolution in the workplace making work from home tasks to be a daily routine these days.

Out of the blue, it has also made a non-reader search for news and updates regarding COVID. Now we are eagerly looking out for news like ever before. In the process, we are hearing many things and principles which help contain the spread of COVID from our daily WhatsApp messages to Facebook feeds, and today I am going to talk about Herd Immunity, which has been followed by many countries at an initial stage of the pandemic and now touted to be the way forward.

What does herd immunity mean?

Herd immunity can be simply defined as the obtained indirect protection from a contagious infectious disease that happens when a specific population is immune either through vaccination or immunity developed through the previous infection of the same disease.

This implies that even those people who are not vaccinated for the disease, or those in whom the vaccine doesn’t trigger immunity, are protected as people around them who are immune can act as barriers between them and an infected individual. Once herd immunity has been established in place for a while, the ability of the disease to spread is lowered significantly, the disease can eventually be eliminated.

How is it calculated for a specific disease?

Herd immunity comes into play only when a specific percentage of the population is immune to the disease and this minimum percentage of the population that would trigger herd immunity is called the Threshold Population.

The threshold population is not a constant and it varies for disease to disease based on the Reproduction number, also referred to a R0.

It represents the number of people that get infected by one contagious/infected person in a community of unprotected individuals.

The threshold population can be calculated by using the following formula:

Herd Immunity Threshold = 1–1/ R0

Percentage of threshold Population = {1–1/ R0} * 100

Now, let us say that COVID is spreading in such a way, if the one COVID infected person is infecting 3 others, the R0 value would be 3. Hence by substituting the same in the above formula we can say that 66% of the population should be immune to COVID to let herd immunity work for COVID.

As cited on The Print as of July 20th the R0 value of India is around 1.17, from which we can infer using the formula that around 15% is the threshold population are required to trigger herd immunity in India.

Key Takeaway: The more infectious the disease is hard it is to attain herd immunity.

How to achieve herd Immunity?

There are two ways to achieve Herd Immunity.

One is through Vaccination and the other is by natural infection.

By Vaccination:

A viral vaccine which causes COVID-19 would be an ideal approach to achieve immunity for herds. Vaccines develop immunity by not causing either disease or complications. Herd immunity enables the population to be safe from disease, including those unable to be vaccinated, such as newborns or those with compromised immune states. Using the Herd immunity principles, the vaccines have been successfully contained the spread of deadly infectious diseases including smallpox, measles, diphtheria, Rubella, plus a lot more.

Often it takes vaccination to achieve herd immunity, but it also has its own set of disadvantages.

  • Protection against certain vaccines can fade off over time, causing revaccination to be needed. Often people do not get the shots they need to be safe from being resistant.
  • Some citizens may also have an objection to vaccines because of Religious reservations, perceptions of future threats, or skepticism.
  • Additionally, if the threshold population drops the limit there will be an exponential spread of the disease.

An example of this would be the recent resurge in the cases of Measles in several parts of the world including the United States of America (The 2019 measles outbreak at Disneyland) due to low vaccination rates.

By Natural Infection:

Herd immunity can also be attained if enough people in the population have recovered from a disease and have developed antibodies against future infection.

For Example, those who recovered from 1918 Flu infection, were found to be immune to the H1N1 Virus (Swine Flu), which is a subtype of Influenza A virus.

Are there any examples of the cases where herd immunity worked like a charm?

  • People in Norway successfully developed partial herd immunity to the H1N1 virus (swine flu) through vaccinations and natural immunity. Similarly, in Norway, influenza was projected to cause fewer deaths in 2010 and 2011 because more of the population was immune to it.
  • Herd Immunity also helped curb many infectious diseases such as smallpox, measles, diphtheria, Rubella

Scientists are concerned about formulating an efficient vaccine. Meanwhile, since much of the population remains uninfected with SARS-CoV-2, it may take some measures to avoid explosive outbreaks such as those we have seen in places like New York City. The physical distancing measures needed can vary over time and need not always be as strict as our current restrictions. Yet unless we want to get infected with SARS-CoV-2 by hundreds of millions of people (what it would take to create herd immunity in the country), life is unlikely to be fully “natural” again before a vaccine can be developed and widely distributed.

Although the concept of Herd Immunity would serve as an efficient barrier to ward off COVID19, the ways in which that can be attained are difficult and in some ways, it may backfire and even worsen the condition.

For example, Sweden and UK governments chose to attain herd immunity by not opting for LockDown hoping the natural infection can help achieve Herd immunity, which surprisingly hasn’t worked as expected causing high death rates and infection surges, mandating the Lockdown later.

Keep checking on us for more curated and handpicked science and health articles.


Herd Immunity: What It Means for COVID-19

What is Herd Immunity and How Can We Achieve It With COVID-19? — COVID-19 — Johns Hopkins Bloomberg School of Public Health

What is herd immunity? | Gavi, the Vaccine Alliance

Importance of Herd Immunity | Breed Street Clinic


Image Credits are with respective owners and the images were taken from Google for representation.


Gopala Krishna Varshith,



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