Dating first cases of COVID-19

Author summary While the COVID-19 pandemic continues, questions still persist as to its origins. Evidence is building that its origin as a zoonotic spillover occurred before the officially accepted timing of early December, 2019. We date the origin of COVID-19 cases from 203 countries and territories using a model from conservation science. We use a method that was originally developed to date the timing of extinction, and turn it to date the timing of origination using case dates rather than sighting events. Our results suggest that the virus emerged in China in early October to mid-November, 2019 (the most likely date being November 17), and by January, 2020, had spread globally. This suggests a much earlier and more rapid spread than is evident from confirmed cases. In addition, our study provides a new approach for estimating dates of the arrival of infectious diseases in new areas that can be applied to many different situations in the future. Questions persist as to the origin of the COVID-19 pandemic. Evidence is building that its origin as a zoonotic spillover occurred prior to the officially accepted timing of early December, 2019. Here we provide novel methods to date the origin of COVID-19 cases. We show that six countries had exceptionally early cases, unlikely to represent part of their main case series. The model suggests a likely timing of the first case of COVID-19 in China as November 17 (95% CI October 4). Origination dates are discussed for the first five countries outside China and each continent. Results infer that SARS-CoV-2 emerged in China in early October to mid-November, and by January, had spread globally. This suggests an earlier and more rapid timeline of spread. Our study provides new approaches for estimating dates of the arrival of infectious diseases based on small samples that can be applied to many epidemiological situations.