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Journal of Allergy and Infectious Diseases

ISSN: 2692-6334

Commentary Open Access
Volume 1 | Issue 2 | DOI: https://doi.org/10.46439/allergy.1.008

Basic reproduction number, effective reproduction number and herd Immunity: Relevance to opening up of economies hampered by COVID-19

Srinivas Mantha1,*
  • 1Research Consultant & Pain Physician, Division of Pain Medicine, Mantha Heart Clinic, Barkatpura, Hyderabad, India
+ Affiliations - Affiliations

Corresponding Author

Srinivas Mantha, smantha@srinivasmantha.com

Received Date: July 01, 2020

Accepted Date: August 18, 2020

Citation:

Mantha S. Basic reproduction number, effective reproduction number and herd Immunity: Relevance to opening up of economies hampered by COVID-19. J Allergy Infect Dis 2020; 1(2):32-34.


Copyright: © 2020 Mantha S. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Abstract

Several countries are in different phases of safely lifting the lockdowns necessitated by the Covid-19 pandemic and re-opening their economies. As they do so, it is important for authorities to recommend or impose some public health measures like social distancing and wearing face masks. Scientific articles are appearing in peer reviewed medical journals and even in the lay press on this topic. Some of the scientific definitions used in these articles might be erroneous. It is therefore necessary for the scientific community to highlight these errors, so as not to convey the wrong meaning.  The purpose of this article is to highlight the importance of correct usage of scientific definitions.  Scientific definitions of basic reproduction number (R0), effective reproduction number (Re) and herd immunity are necessary to correctly understand the epidemiological basis for measures to control the COVID-19 outbreak.  R0 is defined as expected number of secondary cases produced by a single (typical) infection in a completely susceptible population.  R0 is essentially the ratio between transmission rate and recovery rate.  The transmission rate in turn is determined by the rate of contacts in the host population and the probability of infection being transmitted during the contact.  Recovery rate is a reciprocal of duration of infectiousness. Re is defined as expected number of secondary cases produced by a single infection in a population that is made up of both susceptible and non-susceptible hosts.  Re is given by the formula: Re= R0 · (S/N), where S is the number of “susceptible” individuals and N is the total number of all individuals, i.e. susceptible, exposed, infected, and recovered. Herd immunity (actually ‘herd protection’) occurs when a significant proportion of the population is immune by some mechanism, usually by vaccination, resulting in protection for susceptible individuals who are not immune. Care must be taken not to use R0 and Re interchangeably as they have distinct implications with regard to control measures. Relying on herd immunity without vaccination is not a scientific solution in these circumstances.

Keywords

COVID-19, Epidemiology, Basic reproduction number, Effective reproduction number, Herd immunity, Community transmission, Face shields, Universal airborne precautions

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Basic reproduction number, effective reproduction number and herd Immunity: Relevance to opening up of economies hampered by COVID-19

Several countries are in different phases of safely lifting the lockdowns necessitated by the Covid-19 pandemic and re-opening their economies. As they do so, it is important for authorities to recommend or impose some public health measures like social distancing and wearing face masks. Scientific articles are appearing in peer reviewed medical journals and even in the lay press on this topic. Some of the scientific definitions used in these articles might be erroneous.

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