French testing system missed 9 of 10 COVID-19 cases after first lock-down On December 21, Nature published a peer-reviewed accelerated article titled, “Under-detection of cases of COVID-19 in France threatens epidemic control.” In the paper, epidemiologists and data scientists led by Giulia Pullano use mathematical modelling to chart the estimated spread of the virus in France over seven weeks—from the end of lock-down measures, on May 11, to June 28. They compare this estimated spread of the virus to the recorded cases to measure the effectiveness of France’s test and trace system in this period. During this period, Santé publique France (the public health system) recorded a few hundred cases a day. However, the authors estimate that France’s testing system missed around 90,000 symptomatic COVID-19 infections. This amounts to 86 percent of symptomatic cases. As many cases are asymptomatic, however, the true rate of detection in this period was likely well under 10 percent.