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

We searched PubMed, BioRxiv, and MedRxiv for articles published in English from inception to Feb 20, 2020, with the keywords 2019-nCoV, novel coronavirus, COVID-19, SARS-CoV-2 AND reproduction number Italy, Italy transmission. We found several estimates of the basic reproduction number (R 0 ) of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), including average exponential growth rate estimates based on inferred or observed cases at a specific time-point and early growth of the outbreak. However, we identified no estimates of how R 0 had changed in Italy since control measures were introduced in March or estimates that jointly fitted data within Wuhan and Italy and no estimate of secondary effects in Italy. Added value of this study In our study we estimate how transmission has varied over time in Italy, identify a decline in the reproduction number in late as a function the introduction of large scale control measures, and show the potential implications of estimated secondary effects. Implications of all the available evidence SARS-CoV-2 is currently showing sustained transmission in Italy, with substantial risk of outbreaks in different areas. However, the implement of rapid technologies during screening phase can largely influence the value of the reproduction number and support a (partial) relaxation of the isolation measures without introducing a large risk of secondary outbreaks.