reproductive number (Rt)

Syllable breakdown

Dictionary meaning

the effective reproductive number Rt is a time-varying measure of the average number of secondary infections generated by a single infectious individual in a population at time t, distinguishing it from the basic reproduction number R0 which assumes a fully susceptible population with no interventions; when Rt exceeds 1 an epidemic is growing, when it equals 1 it is stable, and when it falls below 1 the epidemic is declining; Rt is estimated in real time from case counts, hospitalisation data, and genomic surveillance, and is widely used by public health authorities to calibrate the intensity of interventions such as social distancing measures, vaccination programmes, and testing and isolation protocols; changes in Rt reflect the combined effects of population immunity, behavioural change, variant emergence, and public health measures