Rt = 2.7

HK01於2020報導︰「港大公共衞生學院流行病學和生物統計學分部主任高本恩表示，當即時繁殖率高於1時，代表每天確診數字會逐步上升，持續時間可能以周計。」

Explanation of the time course of an epidemic can be partly achieved by estimating the effective reproduction number, R(t), defined as the actual average number of secondary cases per primary case at calendar time t (for t >0). R(t) shows time-dependent variation due to the decline in susceptible individuals (intrinsic factors) and the implementation of control measures (extrinsic factors). If R(t)<1, it suggests that the epidemic is in decline and may be regarded as being under control at time t (vice versa, if R(t)>1). 

Chowell, G. (2009). Mathematical and Statistical Estimation Approaches in Epidemiology. Springer.

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Effective reproduction number at time (Rt) is the average number of secondary cases per one case at any given time. This number will vary as the outbreak progresses, and indicates real-time transmissibility. Effective control measures and behavioral changes, such as quarantine enforcement, usage of face masks, travel restrictions, class suspensions, and social distancing, are all factors that may affect the Rt of a virus.

If Rt = 1, each infected patient will go on to infect one other person. Statistically, this would mean that one new infected patient will replace another who had recovered or passed away from the disease. This also suggests that the outbreak is stabilizing, with no changes in number of infected people over time.