CDC说论文是回顾性研究
https://www.nejm.org/doi/full/10.1056/NEJMoa2001316

结论部分有这么段话

We estimated an R0 of approximately 2.2, meaning that on average each patient has been spreading infection to 2.2 other people. In general, an epidemic will increase as long as R0 is greater than 1, and control measures aim to reduce the reproductive number to less than 1. The R0 of SARS was estimated to be around 3,12 and SARS outbreaks were successfully controlled by isolation of patients and careful infection control.13 In the case of NCIP, challenges to control include the apparent presence of many mild infections14 and limited resources for isolation of cases and quarantine of their close contacts. Our estimate of R0 was limited to the period up to January 4 because increases in awareness of the outbreak and greater availability and use of tests in more recent weeks will have increased the proportions of infections ascertained. It is possible that subsequent control measures in Wuhan, and more recently elsewhere in the country as well as overseas, have reduced transmissibility, but the detection of an increasing number of cases in other domestic locations and around the world suggest that the epidemic has continued to increase in size.

我理解的，R0就是人传人的风险性，越高传染性越大
他们算出来2.2，意味着平均每个病人都在向其他2.2人传播感染
文中说，对R0的估计仅限于1月4日之前的发病数据
理解有错吗？也就是说1月4日之前的数据不止能确定人传人，连传播风险都算出来了
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FROM 111.205.170.*