Spark
Loading...

Basic and Effective Reproductive Numbers (R0, Re)

← Builds on Herd Immunity and Vaccine Effectiveness

Terms you will need

  • r0R0 is a number that shows how many people, on average, one sick person will infect in a group where everyone can get the disease.
  • reRe is the average number of people one sick person will infect in a group where some people are already immune or protected.
  • reproductive numberThe reproductive number is a measure of how many new infections one case of a disease causes in a population.
  • basic reproductive numberThe basic reproductive number is the average number of people who will catch a disease from one infected person in a population where everyone is susceptible.
  • effective reproductive numberThe effective reproductive number is the average number of people who will catch a disease from one infected person in a population where some people are already immune.
  • herd immunity thresholdThe herd immunity threshold is the minimum percentage of a population that needs to be immune to a disease to stop its spread.

How this topic runs

  1. 1Start here
  2. 2How it works
  3. 3At competition depth

The basic and effective reproductive numbers, R0 and Re, are key concepts in epidemiology used to understand how contagious diseases spread through populations. R0, or the basic reproduction number, represents the average number of people who will catch a disease from one infected person in a completely susceptible population. It indicates whether a disease can spread: if R0 is greater than 1, the disease can spread, but if it is less than 1, it will likely die out. Re, or the effective reproduction number, adjusts R0 to reflect real-world conditions, such as immunity in the population or public health interventions. Understanding R0 and Re helps scientists and public health officials determine how contagious a disease is, how much of the population needs to be immune to prevent outbreaks, and how effective interventions like vaccination or social distancing can be in reducing transmission.

Figures (2)

R 0 {\displaystyle R_{0}} is the average number of people infected from one other person. For example, Ebola has an R 0 {\displaystyle R_{0}} of two, so on average, a person who has Ebola will pass it on to two other people.
Graph of herd immunity threshold vs basic reproduction number with selected diseases

R0 and Re are numbers that show how contagious a disease is. It tells how many people, on average, one sick person will infect in a population where no one is immune. It updates R0 to show what happens in real life.

Re includes things like people who are already immune or actions like social distancing that slow the spread. When Re drops below 1, the disease will stop spreading on its own. They can show how many people need to be immune to stop a disease.

Key Points

  • R0, or the basic reproduction number, is the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection.
  • Re, or the effective reproduction number, is the number of cases generated in the current state of a population, which does not have to be the uninfected state.
  • The basic reproductive number, denoted R0, is the expected number of cases directly generated by one case in a population where all individuals are susceptible to infection.
  • The effective reproductive number, denoted Re, is the number of cases generated in the current state of a population, which does not have to be the uninfected state.
  • The herd immunity threshold is the critical proportion of the population needed to be immune to stop the transmission of disease, calculated from the basic reproduction number R0.

Terms

Tap a term for a plain-language explanation.

Sources & licensing(4)