Coronavirus’s ability to mutate underestimated, affects deadliness of strains

The article makes the strong claim that it is "confirmed for the first time with laboratory evidence that certain mutations could create strains deadlier than others." If true, this might help to reconcile the disparate estimates of infection rates and lethality in different locales. The underlying paper (which I haven't read yet) is here:

Patient-derived mutations impact pathogenicity of SARS-CoV-2

Hangping Yao, Xiangyun Lu, Qiong Chen, Kaijin Xu, Yu Chen, Linfang Cheng, Fumin Liu, Zhigang Wu, Haibo Wu, Changzhong Jin, Min Zheng, Nanping Wu, Chao Jiang, Lanjuan Li

https://www.medrxiv.org/content/10.1101/2020.04.14.20060160v...