Epidemiology & Public Health

Intermediate

Effective Reproduction Number

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

Formula

R_e = R_0 \times S

Live Calculator

Members

Variables

R_eEffective reproduction number

R_0Basic reproduction number

SFraction of the population still susceptible

Example

R₀ = 3, 40 % immune (S = 0.6) → Rₑ = 1.8

Did You Know?

When Rₑ drops below 1, the outbreak shrinks — this is the goal of every vaccination and lockdown strategy.

epidemiology effective r reproduction pandemic

Share this formula

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.

Basic Reproduction Number

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

Herd-Immunity Threshold

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

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.