Estimate of the development of the epidemic reproduction number Rt from Coronavirus SARS-CoV-2 case data and implications for political measures based on prognostics

Sahamoddin Khailaie; Tanmay Mitra; Arnab Bandyopadhyay; Marta Schips; Pietro Mascheroni; Patrizio Vanella; Berit Lange; Sebastian Binder; Michael Meyer-Hermann

To estimate R2, one needs to know the duration for which an individual remains in a latent noninfectious stage following the transmission of COVID-19 (inverse of this gives R2), whereas R3 can be estimated as the inverse of the period of being infectious before disease onset. If it is assumed that subsequent infections can occur at random during the infectious period before the onset of symptoms, then the average serial interval will be the sum of the average latent period (from infection to infectiousness) and half the average infectious period before disease onset. Hence, we can state the following equations: We know that the mean incubation period for COVID-19 is 5.2 days . The mean serial interval is estimated to be 4 days in one study from a total of 28 infector-infectee pairs (Nishiura et al. 2020 ) and 4.4 days in another study based on data from 21 infection chains in Hong Kong . For our calculation, we have used the mean of these two studies as our average serial interval, which is 4.2 days. Using the above equations for the serial interval and incubation period, we have calculated the values of 1/R2 and 1/R3, which provide us with a median value of 2 days for 1/R2 and 3.2 days for 1/R3. Further assuming that a person once exposed to the infection, spends at least one day in latent non-infectious period and overall, the latent noninfectious period (1/R2) is not greater than latent infectious period (1/R3), we get a range of 2.6 to 4.2 days for 1/R3. To calculate the corresponding value of 1/R2, we make use of the median incubation period (1/R2 + 1/R3) of 5.2 days.