Epidemiology & Public Health

Intermediate

Basic Reproduction Number

Average number of secondary infections produced by one infected individual in a fully susceptible population.

Formula

R_0 = \beta \times D

Variables

R_0Basic reproduction number

\betaTransmission rate (contacts × probability per contact)

DDuration of infectiousness

Example

β = 0.5/day, D = 4 days → R₀ = 2

Did You Know?

Measles has one of the highest R₀ values ever recorded — between 12 and 18 — meaning one case can spark a dozen more.

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More in Epidemiology & Public Health

Incidence Rate

Rate at which new cases of a disease appear in a population over a given period.

Prevalence

Proportion of a population that has a particular condition at a point in time.

Herd-Immunity Threshold

Minimum fraction of the population that must be immune to prevent sustained spread.

Effective Reproduction Number

Actual average infections per case when part of the population is already immune.

SIR Model — Susceptible

Rate of change of the susceptible population in the SIR compartmental model.

SIR Model — Infected

Rate of change of the infected population — new infections minus recoveries.