Based on her analysis, Professor Stadler said the virus likely infected between 4,000 and 19,000 people on January 23, when Wuhan was quarantined from the rest of China.
At the time, however, the official count of confirmed infections only stood at 581.
As a result, the epidemiologist said only one in 33 infections appeared in official reports, at the most extreme end of the spectrum.
A more positive estimate suggests only one in seven cases were officially reported.
Using genetic data, Professor Stadler also looked at how infectious the coronavirus is.