Summary
R0 is the average number of new infections one case causes in a fully susceptible population.
In depth
R0 depends on transmissibility, contact rate and infectious period. If R0 is above 1, spreads; below 1, dies out. Rt is the effective number during an outbreak, lowered by immunity and measures.
R0 is not fixed; it depends on behaviour and population. Control aims to bring effective R below 1. Superspreading events create heterogeneity.
Key idea: reducing contacts or susceptibility lowers R.
R0 estimates for measles are 12 to 18, for the original SARS-CoV-2 about 2 to 3, for Omicron higher, for influenza 1 to 2 and for Ebola around 1.5 to 2. R0 applies to a fully susceptible population; in real situations the effective reproduction number Rt matters, which changes with immunity, behaviour and interventions. The herd immunity threshold is 1 minus 1/R0.
Dispersion matters too: with overdispersion (parameter k), a few people cause most infections, so superspreading events are key and targeted measures work. Generation time influences speed of growth. Estimates come with uncertainty and depend on methods.
Remember: R0 is not a fixed property of the virus alone, since it depends on the population and how people mix.
Frequently asked questions
What is Basic Reproduction Number?
R0 is the average number of new infections one case causes in a fully susceptible population.
Which area of biology covers Basic Reproduction Number, and how advanced is it?
Basic Reproduction Number is one of the 52 topics in Immunology & Disease. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Mathematical Epidemiology, Herd Immunity, Infectious Disease Transmission.
Can you give an example of Basic Reproduction Number?
Measles R0 about 12 to 18; seasonal flu about 1.3.
What should I learn before Basic Reproduction Number?
Work through the Beginner topics in Immunology & Disease first, such as Immune System, Viruses, Innate Immunity, then return to Basic Reproduction Number. Intermediate topics assume the Beginner vocabulary.
What topics are related to Basic Reproduction Number?
The closest topics to Basic Reproduction Number are Mathematical Epidemiology, Herd Immunity, Infectious Disease Transmission, Virus Evolution. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Basic Reproduction Number?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Basic Reproduction Number. To practise the whole of Immunology & Disease, use the Immunology & Disease quiz.
How is Basic Reproduction Number different from Mathematical Epidemiology?
Basic Reproduction Number: R0 is the average number of new infections one case causes in a fully susceptible population. Mathematical Epidemiology: SIR and related compartment models predict epidemic dynamics and the effect of interventions. Read both side by side and note what each one explains.
How should I study Basic Reproduction Number step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Mathematical Epidemiology and explain the difference aloud. Finally, take the Immunology & Disease quiz and come back to this page for any question you miss.