As previous evidence indicated, the Delta VOC is highly transmissible. As of July 13, 2021, Delta variant has been reported in at least 111 countries and regions worldwide (WHO weekly epidemiological update on COVID-19 - July 13, 2021). A recent study, based on data available by June 2021, projected that the Delta VOC would rapidly surpass other SARS-CoV-2 variants and soon become the dominant circulating lineage (Campbell et al., 2021). In the past few days, the Centers for Disease Control and Prevention (CDC) announced that the Delta variant, replacing the Alpha variant (B.1.1.7), had become the predominant SARS-CoV-2 lineage in the United States (US). It was estimated that the proportion of COVID-19 cases attributed to the Delta variant in the US was around...