We believe the actual number of 2019-nCoV cases in mainland China is likely much higher than that reported to date. Specifically, we estimate there to be around 58,000 cumulative cases of 2019-nCoV in mainland China by the end of January (as of January 31, the reported cases are close to 12,000). This estimate is in line with our previous analysis on January 25, which estimated the proportion of reported to estimated cases to be close to 10%.
It is likely that part of this discrepancy is due to reporting delays. However, the substantially larger number of estimated cases suggest a majority of the cases may be mild (or asymptomatic), do not require seeking medical care, and thus are not reported. Furthermore, based on this analysis, we believe the outbreak began in November, and there were already hundreds of human cases of 2019-nCoV in Wuhan in early December. The estimated verses confirmed cases during January are presented below.