Why Herd Immunity Is Still A Long Way Ahead For TN?

In early 2020, during the initial phase of the Covid pandemic in India, a lot was discussed about herd immunity and how it would drastically bring down the number of cases. Over a year later, we are still far from achieving it. What are the complexities of achieving herd immunity against Covid and why a great deal remains to be done?

- Sushmitha Ramakrishnan

Why is it important?

Herd immunity, also known as population immunity, is the indirect protection from an infectious disease that happens when a population is immune either through vaccination or immunity developed through the previous infection. When enough people (threshold population) have immunity against Covid, it would significantly reduce the rate of spread and contain transmission within smaller pockets of location. Effectively, it will restrict the pandemic.

In Tamil Nadu, about 23 lakh people have tested Covid positive and almost 22 lakh have been vaccinated. This means that only about 6.4 per cent of the seven crore people in the State have immunity against Covid. “We need at least four crore people in the State to be vaccinated, in order to approach herd immunity,” said Dr. P Kuganantham, a senior epidemiologist.

Early studies estimated that if 60 to 70 per cent population was immune to Covid, we would reach herd immunity. This has changed since. The current estimates require 85 to 95 per cent of people to become immune, according to the World health Organisation. What caused this change?

The mutating virus