傳染病的嚴重程度，是用R0和Rt值來衡量。
R0和Rt值的定義為：
One measure of viral spread is the R0, the expected number of secondary infectious cases produced by a primary infectious case. This calculation is used to determine the potential for epidemic spread in a susceptible population. The effective reproduction number, Rt, determines the potential for epidemic spread at a specific time t under the control measures in place (Figure 1). To evaluate the effectiveness of public health interventions, the Rt should be quantified in different settings, ideally at regular and frequent intervals (eg, weekly).*
簡單中譯：R0 是指首位感染者會傳染給多少人。Rt值是指在特定時間內(t)，一位染病的病患，平均可以傳染給多少人。(在實務上所謂的特定時間，一般是用每7天的區間來計算，所以Rt就可以用來衡量防疫措施的有效性。)
2021/5/31 公告台灣COVID-19的Rt值，已經從疫情在5/13-5/15最嚴重時的15降到了1.02；從1個人平均可以傳染給15人進步到1個人可以傳染給約1人，足見防疫的初期效果已經出現。然而，病毒的感染，本來就不是線性的，我們還得步步為營。
現在，大家都知道疫苗是根本的重點，這很好。如何及早備足打好安全的疫苗，絕對是接下來最重要的防疫課題。
*:〈Public Health Measures and the Reproduction Number of SARS-CoV-2〉，JAMA network 網站
P.S. 附圖亦來自〈Public Health Measures and the Reproduction Number of SARS-CoV-2〉一文
2021/5/31 Rt Damakey
