>Overall, our findings indicate that a large proportion of COVID-19 infections were undocumented prior to the implementation of travel restrictions and other heightened control measures in China on 23 January, and that a large proportion of the total force of infection was mediated through these undocumented infections (Table 1). This high proportion of undocumented infections, many of whom were likely not severely symptomatic, appears to have facilitated the rapid spread of the virus throughout China. Indeed, suppression of the infectiousness of these undocumented cases in model simulations reduces the total number of documented cases and the overall spread of SARS-CoV2

This paper is about undetected carriers spreading SARS-CoV2 across China prior to the Jan 23 lockdown. It does not imply that 86% of all total infections that we see currently are undocumented, it only reflects the relatively narrow testing that was happening prior to Jan 23 (likely only the severe cases).

After Jan 23, China expanded its testing much more broadly, and other countries (such as South Korea) have done so as well. You should not take this paper to mean that the actual number of cases for these countries is larger by a factor of 1/(1-0.86).