When the drug company Biogen held a conference at a Boston hotel on Feb. 26-27, the US had a grand total of 15 coronavirus cases on the books, notes the Washington Post. That would change quickly, of course, and a new study demonstrates how events like this international conference helped COVID-19 establish its foothold. In a massive genomic research project, scientists estimate that this single get-together was responsible for 20,000 coronavirus cases in four counties of Massachusetts by early May, reports the Boston Globe. Of particular note: They traced this version of the virus to a large outbreak among Boston's homeless community just a few weeks later, per WBUR, though how it made its way from the conference to the city's homeless shelters isn't clear.
“We’re not trying to point fingers,” says Bronwyn MacInnis of Broad, Brigham and Women’s Hospital, one of the authors of the study. “The circumstances of this event—the fact that it happened so early in the epidemic and the timing of where we were with COVID in the public consciousness—meant it had a disproportionate effect." The 20,000 figure is an extrapolation, but scientists not affiliated with the study think it's legit. For the study, which hasn't been peer reviewed, researchers analyzed the genetic sequences of the virus in 772 patients and found that 289 of them could be traced to the Biogen conference. That is by far the largest single source, with the rest coming from more than 80 different versions that were introduced to the state. Some versions "fizzle out, others light fires," says MacInnis, and more studies like these might help scientists figure out how and why. (Read more coronavirus stories.)