Co-circulation of SARS-CoV-2 Alpha and Gamma variants in Italy, February and March 2021

Background Several SARS-CoV-2 variants of concern (VOC) have emerged through 2020 and 2021. There is need for tools to estimate the relative transmissibility of emerging variants of SARS-CoV-2 with respect to circulating strains. Aim We aimed to assess the prevalence of co-circulating VOC in Italy and estimate their relative transmissibility. Methods We conducted two genomic surveillance surveys on 18 February and 18 March 2021 across the whole Italian territory covering 3,243 clinical samples and developed a mathematical model that describes the dynamics of co-circulating strains. Results The Alpha variant was already dominant on 18 February in a majority of regions/autonomous provinces (…