Sebastian Funk, Sam Abbott and Johannes Bracher's discussion contribution to the papers in Session 2 of the Royal Statistical Society's Special Topic Meeting on Covid‐19 Transmission: 11 June 2021.

Any assessment of the quality of I R i SB I t i sb estimates would thus involve a decision on the timescale at which the reproduction number is considered and what exactly I R i SB I t i sb represents and whether models agree that this is being estimated. For example, consider the following discrete-time branching process model, initialised with some starting number of infectious individuals I I i SB I 0 i sb , a mean reproduction number I R i and over-dispersion I k i : I I i SB I t i sb ~ Poisson ( SB I t i sb ). By definition of the instantaneous reproduction number I R i SB I t i sb is the average number of new infections caused by infectious individuals at time I t i (weighted by their infectiousness). [Extracted from the article]