The difference between an R0 of three and six is massive. For example, with the original strain of SARS-CoV-2, one person would infect about three people, and each of those people would infect three more. So after only two rounds of transmission, cases would rise by nine (3 x 3 = 9). After three rounds, cases would rise by 27 (3 x 3 x 3 = 27). But with the delta variant, the first person would infect six others, who would each then infect six more people. So after two rounds of transmission, cases would already rise by 36 (6 x 6 = 36). After three rounds, cases would surge by 216 (6 x 6 x 6 = 216).