Herd Immunity - How It Protects A Population From Disease?

Written by Dr. Pramod Mane on Fri, 11 November 2022


Since the COVID pandemic struck, governments around the world have been scrambling to find a solution. Each had a different approach, some tried lockdowns, other tried partial restrictions, while some did seemingly nothing.

We've all heard the phrase 'herd immunity' making the rounds on news channels and the internet, but are not sure what herd immunity means.

We're here to do some myth busting and clear the air surrounding this often-misconstrued phrase.

Firstly, let's clarify the facts on how immunity works, in this case adaptive or acquired immunity. Whenever your immune system comes in contact with a foreign organism or substance, your body tries to fight it. It then develops tools to fight these foreign entities, aside from that your immune system also stores information on these 'invaders'. Because of this process, after you recover, you acquire protection against any subsequent attack from these invaders. This is the reason why you can become immune by recovering from an earlier infection or through vaccination.

What is herd immunity?

Herd immunity sometimes also called community immunity is a form of indirect protection from communicable and infectious disease, it can occur when a sufficient proportion of a population has become immune to an infection. This can be either through vaccination or because of previous infection.  Individuals who are immune to a disease act as a barrier to the spread of disease, and slow or prevent the transmission of the disease to others.

How is herd immunity attained?

A person can acquire immunity either by natural infection or immune response can be prompted artificially by means such as vaccination. Our immune   does not distinguish between naturally acquired infections through micro-organisms and artificially synthesized vaccines. They develop an active response to both, so in effect, the immunity induced in us by vaccination is similar or identical to what would have occurred from contracting and recovering from that particular disease naturally. Typically, a vaccine may contain either a portion of the  , or a weakened genetic material from the pathogen.

In order to achieve herd immunity via vaccination, vaccine manufacturers try to produce effective vaccine with as low failure rates as possible.

How does herd immunity work to help protect a population?

Once a person becomes immune, his body This can both slow and stop the spread of a disease. The higher the number of immune individuals in a given group, the lower is the risk that non-immune individuals will come into contact with an actively infectious person.

When a certain critical percentage of the population acquire resistance to a disease, a collective state of     or herd immunity level is obtained. Thereby, reducing the likelihood of infections in people who lack immunity. When this happens on a large scale, the herd immunity threshold may be reached and the disease may no longer persevere and thus cease to be endemic.

It is important to remember, that the percentage of immunised people required to curb the spread of infection and achieve herd immunity levels varies from disease to disease.

It is estimated that at least 90-95% of people need to be immunised against some disease like measles to obtain true herd immunity.  . Similarly, for polio and diphtheria, 85% and 80-86% population should be vaccinated respectively.

Protect the vulnerable!

In any population, there are bound to be some people who either don't develop immunity after being vaccinated, or for some reason or the other cannot be vaccinated. This includes, new-borns, immune deficient people and the elderly. When we achieve herd immunity, it confers protection to these otherwise vulnerable groups.

We've done this before!!

Over the course of human history, many diseases have ailed us, but due to widespread immunisation, we've been able to largely eliminate some of these otherwise crippling and deadly diseases. An example of this is Polio. At its peak it disabled almost everyone who encountered it.

Because of the prompt and co-ordinated efforts of governments and people around the world we've been able immunise a very large proportion of the global population and have effectively mitigated the risk of contracting it.

Let's not forget the Flu, at one point it swept the world   populations, but as more people contracted it and gained immunity, longer poses as a major life-threatening risk. At most, in otherwise healthy people, it results in a week or two of sniffles and a head cold.

Some other examples of diseases that were once endemic and common place but no longer pose a serious threat to us are Measles, Pertussis and Mumps. This is not because they are any less contagious than they used to be, but because a majority of us have been immunised against these diseases and therefore have reached the critical levels of immunity required to garner and secure herd immunity.

Although this pandemic we're in may seem never ending and tragic, through mass vaccination and immunisation we can help our most vulnerable. So, for the sake all the people we hold dear, and for ourselves, let's get vaccinated folks!


Dr. Pramod Mane

A Doctor of Medicine (MD) in Pharmacology., currently based in Mumbai, India, Dr Pramod Mane, comes with an experience of more than 20 years of working in Medical Affairs in the Pharmaceuticals & Nutraceutical Industry. Director of Medical Services at Mega Lifesciences since 2008, Dr Mane has been associated with several MNCS in the areas of Medical Affairs, Medical Services, Medico-marketing, Pharmacovigilance & Clinical trials in his illustrious career.

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