Metodos Matematicos da Fisica

South Korea has a case data with two series: (a) day 1 to 30 (\(1\leq N\leq 30\)), fitted curve $Z_{a}$ (green line in Figure Cases-South Korea), and (b) day 31 and after ($N\geq 31$), fitted curve $Z_{b}$ (blue line in Figure Cases-South Korea). These two series are quite different from the Chinese two subseries, where there is a global fitting curve (see Figure Cases-China). As we can see in Figure Cases-South Korea, the thin red curve ($Z_{73}$) does not fit properly the whole data. A second wave of Covid-19 cases is in progress in South Korea (blue line $Z_{b}$ in Figure Cases-South Korea). Fortunately, this second wave is flattening. An important lesson can be learned here: a second wave of case infections can come very fast.