A study of SARS-CoV-2 evolution in Italy: from early days to secondary effects after social distancing

Marco Claudio Traini; Carla Caponi; Riccardo Ferrari; Giuseppe Vittorio De Socio

(A) Scenario (A) refers to the time-independent SEIR model (cfr. upper panel of Fig. 4 . The effective reproduction number is constant (cfr. Fig. 5 ). With the parameters of table I fitted on the Wuhan outbreak [8] and renormalized to reproduce the early data in Italy [10] , one obtains R 0 ≈ 4.9. The value of c = c 0 = 2 day −1 is rather low compared with the Wuhan rate (c 0 ≈ 15 day −1 ) reflecting the different homogeneities of the two countries and the different social organization. It is shaped on the limited number of contacts after the control measures. The large value of the reproduction number results in a . CC-BY-NC-ND 4.0 International license It is made available under a author/funder, who has granted medRxiv a license to display the preprint in perpetuity. The results take into account the variation in time of the measures and diagnose. In particular the decrease of the contact rate due to lack of contact for people solicited to remain home (see Eq. (9)) and the shortening of the diagnose tests (from 7 days to 8 hours (full curve), see also Eq. 10. The results are compared with a simple (time independent) SEIRmodel including isolation and quarantine [8, 10] Italy has been the first western country involved in the epidemic outbreak SARS-CoV-2. After 39 days (March 30th) the evolution is still a first expanding phase. However after almost 20 days of isolation the perspective of relaxing, at least partially, the distancing measures is appearing in many discussion at different levels.