What is the basic reproduction number R-naught?

Conditions

• Applies to a population where everyone is susceptible.
• Used here as an early-outbreak measure.

Reasoning, step by step

1. Identify the parameter $R_0$ as the basic reproduction number.
2. Recognize that it measures the average number of secondary infections produced by one case.
3. Note the critical condition that the entire population must be susceptible for this specific definition to apply.

Example

The video defines $R_0$ verbally and on-screen as "R-naught = average new infections from one case" with the condition "everyone susceptible".

Common misconceptions

• Believing $R_0$ is a fixed count for every individual rather than a population average.
• Assuming $R_0$ applies when some immunity already exists in the population.

Watch the explanation

Explore next

• Why does R-naught greater than one lead to exponential growth?
• How is R-naught approximated from growth rate and serial interval in the SIR model?