Herd Immunity in India: A Review

Abstract

Herd Immunity is a brilliant solution to tackle and control global pandemics, if taken proper route for immunization such as through vaccination. It is defined as the number of immune individuals against a transmissible virus in a completely susceptible population. The term herd protection or herd effect is the protection to the whole population due to herd immunity. Herd immunity threshold is the minimum proportion of immune population required for herd effect or herd protection. To calculate the threshold, we use basic reproduction number (R0) to measure the rate of transmission of pathogen, in this case SARS-CoV-2. However, a better measure is effective reproduction number (Re). India is major example of herd immunity. Despite strict lockdown and other Covid measure, due to already crowded area the virus could spread fast and to vast majority of people if one of them were to catch it. This explains the steady decline in the number of coronavirus cases in India. At the end, until an approved effective vaccination available, public will still need to follow all the CDC guidelines in order to avoid the large deaths along with natural infection.

Biological Determinants of Emergence of SARS-CoV-2 Variants

“…Originally, with an estimated BRR of 2-3, researchers estimated the proportion of the population needed to be immunized to induce Herd Immunity around 50-67% [31][32][33]. Since then, the emergence of new SARS-CoV-2 variants, most famously the Delta variant, studies suggest a higher BRR (>5) [34,35] than the alpha variant (2-3) [31][32][33][36][37][38][39] increasing the vaccination/immune threshold needed in order to achieve a protective effect. An increase in the necessary number of individuals vaccinated propose additional hurdles in reaching Herd Immunity, with the ever-increasing anti-vax movement or individuals acting as "freeloaders" (i.e., individuals who are not vaccinated, yet expect to be protected by the rest of the community being vaccinated).…”