https://wwwnc.cdc.gov/eid/article/26/7/20-0282_article
I believe the 5.7 R0 represents early in the epidemic in Wuhan, not necessarily what was seen in Europe or the US.
Originally Posted by FTFA
We found R0 is likely to be 5.7 given our current state of knowledge, with a broad 95% CI (3.8–8.9). Among many factors, the lack of awareness of this new pathogen and the Lunar New Year travel and gathering in early and mid-January 2020 might or might not play a role in the high R0.