Immediately after Christian Drosten published a genetic sequence of the novel coronavirus online on 28 February, he took to Twitter to issue a warning. As the virus has raced around the world, more than 350 genome sequences have been shared on the online platform GISAID. They hold clues to how the new virus, named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is spreading and evolving. But because the sequences represent a tiny fraction of cases and show few telltale differences, they are easy to overinterpret, as Drosten realized.
A virologist at the Charité University Hospital in Berlin, he had sequenced the virus from a German patient infected with COVID-19 in Italy. The genome looked similar to that of a virus found in a patient in Munich, the capital of Bavaria, more than 1 month earlier; both shared three mutations not seen in early sequences from China. Drosten realized this could give rise to the idea that the Italian outbreak was “seeded” by the one in Bavaria, which state public health officials said had been quashed by tracing and quarantining all contacts of the 14 confirmed cases. But he thought it was just as likely that a Chinese variant carrying the three mutations had taken independent routes to both countries. The newly sequenced genome “is not sufficient to claim a link between Munich and Italy,” Drosten tweeted.