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

In one Chinese case series of 138 patients [A5], the percentage of hospitalized patients requiring intensive care support was 26%. We assume that this fraction increases with age. We vary ϑ within a range of 0.15 -0.40. α: Currently, there is no reliable data available about the asymptomatic cases. However, we note that about 9% of the confirmed infectious population in Italy remain asymptomatic (Italian data 2020). We can also have an idea about this fraction from the manifestation index (RKI Steckbrief 2020). The manifestation index describes the proportion of those infected who actually fall ill. Three studies from different settings (cruise ship outbreak, evacuated returning travellers, contact-based case search) gave figures of 51% (Mizumoto et al. 2020) , 69% (Nishiura et al. 2020b ) and 81% (Bi et al. 2020) . Hence, in a scenario where extensive tests are not performed and contacts are not traced properly, this fraction could be higher. However, in a setting where contacts have been traced properly, thereby effectively isolating the exposed population in an early stage before they become asymptomatic carriers, and when extensive tests are performed, this fraction would be minimal. As a median value, we assume it to be nearly 9%. We further assume that most of the people will show up symptoms as age increases. We vary α for a range of values from 0.01 -0.16. β: It represents the risk of infection from the infected symptomatic patients as well as captures the risk from all those who are not yet effectively isolated. Therefore, this fraction varies within countries, cultures and healthcare systems. We assume it to be in the range of 0.05 -0.50. In the best-case scenario, this fraction would be zero, which is too unrealistic due to delay in isolating patients. The maximum value of this fraction is 1, which is also unrealistic as it would mean that even after symptoms occur, every patient is free to make contacts with others as before. As a median value, we assume β to be 0.25.