Understanding the Concept of Herd Immunity

Our immunity is what decides the extent to which we fall sick - low immunity means high risk of attracting all kinds of health problems. However, in this article, our specific focus is not ‘immunity’ but rather, ‘herd immunity’, a term which we have all heard of a lot in the post-COVID world that we live in.

When the coronavirus first hit China and then started to spread, almost all of us had normal or low immunity levels. This posed as a great breeding ground for the virus to grow and expand to different parts of the world. This brings us to the main point of this article. How can we develop immunity to become resistant to this virus and its many strains.

What is Herd Immunity?

Herd immunity or population immunity refers to the indirect protection or resistance that we develop from certain infections or diseases. It happens when a population of people is immune from an infection, either via a vaccination or through developed immunity. As per WHO, it is always a better idea to develop herd immunity through vaccinations instead of letting the virus or infection spread throughout the population and then wait for immunity to develop, as this can lead to many deaths and serious cases.

WHO further suggests that herd immunity against COVID-19 should be achieved by preventing cases of infection through vaccinations. Vaccines or shots work towards protecting us by training our immune system to create proteins, also known as antibodies, to fight the infection. The reason why it is preferred is because vaccines do the same for herd immunity that a full blown spread of a pandemic can - only without making people sick. These vaccines can protect the people from getting infected and by preventing the passing of the pathogen.

To Further Understand Herd Immunity

Let’s consider an example of what herd immunity can look like. Suppose 85 percent of a country’s population becomes immune to a certain type of virus, it would mean that 4 out of every 5 people won’t get sick even after encountering someone with the disease or virus. This would result in disease control.

For a population to attain herd immunity, in case of a seriously contagious infection, around 50 to 90 percent of the people need to be immune before the infection rates start falling on the curve. This is what had happened during the outbreak of Zika virus in Brazil when after two years of the outbreak, 63 percent of the population had been exposed to the virus and hence the whole community reached a point of herd immunity.

Does Herd Immunity Work?

Herd immunity works for various illnesses, as research and surveys across the globe suggest. In Norway, people developed herd immunity to the N1H1 virus or swine flu, with proper vaccinations and natural immunity. In the following years, Norway also projected fewer cases of deaths due to influenza because of the increased immunity. While herd immunity can stop the spread of a disease or infection, it can also change without anyone knowing. This is to say it may not always offer protection against all diseases. Some illnesses can only be efficiently prevented by vaccines or proper treatments - one example of it would be tetanus as it spreads in your environment and not through human contact.

It is important to get daily vaccinations as prescribed for even herd immunity to build in a particular place - while it may not protect each and every individual, it will surely help control the spread of disease.

References

●    Coronavirus disease (COVID-19): Herd immunity, lockdowns and COVID-19 (https://www.who.int/news-room/q-a-detail/herd-immunity-lockdowns-and-covid-19)
●    Is the end of Zika nigh? How populations develop immunity (https://sph.med.unsw.edu.au/news/end-zika-nigh-how-populations-develop-immunity)
●    Randolph HE, Barreiro LB. Herd Immunity: Understanding COVID-19. Immunity. 2020;52(5):737-741. doi:10.1016/j.immuni.2020.04.012 (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7236739/)
●    Herd immunity and COVID-19 (coronavirus): What you need to know (https://www.mayoclinic.org/diseases-conditions/coronavirus/in-depth/herd-immunity-and-coronavirus/art-20486808)
●    John TJ, Samuel R. Herd immunity and herd effect: new insights and definitions. Eur J Epidemiol. 2000;16(7):601-6. doi: 10.1023/a:1007626510002. PMID: 11078115. (https://pubmed.ncbi.nlm.nih.gov/11078115/)
●    Community Immunity: How Vaccines Protect Us All (https://newsinhealth.nih.gov/2011/10/community-immunity)
●    Medley GF. Herd immunity confusion. Lancet. 2020;396(10263):1634-1635. doi:10.1016/S0140-6736(20)32167-X (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7581340/)