COVID-19 PANDEMICS: HOW FAR ARE WE FROM HERD IMMUNITY?

HERNANDEZ-SUAREZ, C. M.; MURILLO-ZAMORA, E.; ESPINOZA-GOMEZ, F.

Objectives: to estimate the current number of total infections in a region in order to measure the progress of the epidemic with the purpose of reopening activities and planning the deployment of vaccines. Study design: We recovered estimates of the basic reproductive number (R0) and the Infection Fatality Risk (IFR) as well as the number of confirmed cases and deaths in several countries. Methods: this works presents an expression to estimate the number of remaining susceptible in a population using the observed number of SARS-CoV-2 related deaths and current estimates of R0 and IFR. Results: the epidemic will infect most of the population causing 2.5 deaths per thousand inhabitants on average, and herd immunity will be achieved when the number of deaths per thousand inhabitants is close to two. This work introduces an expression to provide estimates of the number of remaining susceptible in a region using the reported number of deaths. Conclusions: any region with fewer than 2.5 deaths per thousand individuals will continue accumulating deaths until this average is achieved, and the infection rate will exceed the removal rate until the number of deaths is about two deaths per thousand, when herd immunity is reached. Waves may occur in any region where the number of deaths is below the herd immunity level.