The **key difference** between basic and effective reproduction number is that **basic reproduction number (R _{0}) is the reproduction number when there is no immunity from past exposures or vaccination while effective reproduction number (R) is the reproduction number when there is some immunity or some intervention measures in place.**

Infectious diseases easily spread among populations. Some diseases are epidemic while some are pandemic. An epidemic is a regional outbreak of an infectious disease, while a pandemic is a worldwide spread of an infectious disease. Reproduction number is a measure often used to reflect how infectious the disease is. Basic reproduction number (Ro) and effective reproduction number (R) are two epidemiologic matrices used to describe the contagiousness of infectious agents.

### CONTENTS

1. Overview and Key Difference

2. What is Basic Reproduction Number (Ro)

3. What is Effective Reproduction Number

4. Similarities Between Basic and Effective Reproduction Number (R)

5. Side by Side Comparison – Basic vs Effective Reproduction Number in Tabular Form

6. Summary

## What is Basic Reproduction Number (Ro)?

Basic reproduction number or R_{0} is one of the fundamental and most often used metrics in studying infectious disease dynamics. It describes the number of secondary cases an infected person would produce in a completely susceptible population. In other words, it tells the number of cases of a disease one infected person can cause. It is generally reported as a single numeric value or low-high range.

If R_{0} is higher than 1, the outbreak continues because the infected person is expected to infect at least one other person on average. In contrast, if the R_{0 }is less than 1, the outbreak ends because the infected person is less likely to spread the infection. For example, measles, which is an infectious disease, is one of the most contagious infections. The R_{0} value of measles ranges between 12–18. In simple words, one infected person can infect 12 to 18 other individuals in a susceptible population.

R_{0} reveals how much we should be worried about the infection. In addition, this value is useful when estimating the proportion of the population that must be vaccinated in order to prevent the infection.

This value is an indicator of the contagiousness or transmissibility of infectious and parasitic agents. However, there are several factors affecting the R_{0}. They are biological, socio-behavioural, and environmental factors that are responsible for pathogen transmission.

## What is Effective Reproduction Number (R)?

Effective reproduction number or R is the mean number of secondary cases an infected person can cause in a population where there is some immunity or some intervention measures in place. Similar to R0, R can vary across locations. This is because communities in different locations have different levels of immunities. With time, the number of susceptible individuals declines. Moreover, when the control measures are implemented, the infectious nature of the disease declines.

## What are the Similarities Between Basic and Effective Reproduction Number?

- Basic and effective reproduction number are two epidemiologic matrices used to describe the contagiousness of infectious agents.
- Both can vary across locations.

## What is the Difference Between Basic and Effective Reproduction Number?

Basic reproduction number and effective reproduction number are two epidemiological matrices. Basic reproduction number refers to the number of secondary cases one case would produce in a completely susceptible population. Meanwhile, effective reproduction number refers to the average number of secondary cases of an infectious disease arising from a typical case in a population where there is some immunity or some intervention measures in place. So, this is the key difference between basic and effective reproduction number. Most importantly, basic reproduction number occurs in a fully susceptible population, but effective reproduction number occurs in a population where there is some immunity or some intervention measures are in place.

Below is a summary of the difference between basic and effective reproduction number.

## Summary – Basic vs Effective Reproduction Number

R_{0} is when there is no immunity from past exposures or vaccination, nor any deliberate intervention in disease transmission. R is when there is some immunity or some intervention measures are in place. Therefore, basic reproduction number can be defined as the average number of secondary cases of an infectious disease arising from a typical case in a totally susceptible population. Meanwhile, effective reproduction number can be defined as the average number of secondary cases of an infectious disease arising from a typical case in a population where there is some immunity or some intervention measures are in place. Thus, this explains the key difference between basic and effective reproduction number.

##### Reference:

1. “2.2 The Reproduction Number”. Www1.Health.Gov.Au, 2020, Available here.

2. Van den Driessche, Pauline. “Reproduction Numbers Of Infectious Disease Models”. NCBI, 2017, Available here. Accessed 3 Apr 2020.

##### Image Courtesy:

1. “R Naught Ebola and Flu Diagram” By KieraCampbell – Own work (CC BY-SA 4.0) via Commons Wikimedia

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