A single conference back in February 2020 apparently led to more than 300,000 coronavirus cases over the following months, according to a new study published in the journal Science on December 10. Remember when big gatherings were a thing before the pandemic? This is a terribly clear example of why they aren’t anymore.
Here’s what happened: A business conference for the company Biogen took place in Boston from February 26–27, just days before the United States reported its first coronavirus death. The conference, which 175 people reportedly attended, initially led to a cluster of more than 100 coronavirus cases in the following weeks, according to the Massachusetts Department of Public Health. That led to concern that the conference might have been a super-spreader event. For this new study, researchers sequenced the genomes (the complete genetic information) of the SARS-CoV-2 virus from 28 of the conference cases. This confirmed that the viruses’ genomes were highly similar to each other in that narrow timeframe. While SARS-CoV-2 is just one virus, viral genomes change constantly. The genomes in these 28 conference cases being so similar was a sign that these cases were connected.
Upon further analysis, researchers learned that two of the genomic markers involved in these cases hadn’t been seen in the U.S. until the Biogen event. They could trace one of them back to Europe, but there was no evidence of the other in any public genome databases prior to the conference. These unique markers gave researchers a way to track just how far this single super-spreader event could go.
It turns out, a long way. By the end of the study period in November, the Boston area’s four counties had reported 51,718 coronavirus cases; between 30% and 46% of the genomes among them were traceable back to the Biogen conference cases. By November 1, 29 states had coronavirus cases with genomic markers linked to the SARS-CoV-2 present at the conference, according to the study, and those markers were also found in cases in Australia, Sweden, and Slovakia.
Ultimately, the researchers estimate that more than 300,000 coronavirus cases contain either of the genomic markers they’re connecting back to contagion at this one event—some 71,000 of them in Florida alone. In fact, contagion at that single event may be the origin point for as many as 1.6% of all cases in the United States, as the Boston Globe reports.
In a statement, Biogen said it hoped that this research would “continue to drive a better understanding of the transmission of this virus and efforts to address it” and that the coronavirus has had a “very direct and personal impact” on the company, according to the Associated Press.
To be clear, this is just one study, and we’ve seen how quickly the science on coronavirus moves—it’s an ever-shifting target. The study also had limitations, like the fact that the database they used for genomic sampling isn’t a random sampling of coronavirus in the U.S., so these estimates could be biased in some way. But as it stands now, this study hints at just how critical the public health measures against coronavirus have been and why they must continue. Wherever people gather—an indoor wedding in Washington, a Canadian spin class, or an international conference in Boston—this virus can go haywire. Given the contagious nature of the virus and the possibility of asymptomatic spread, the effects go far beyond the people who actively take part in these gatherings, as a summer wedding in Maine that led to the death of seven people who never attended can attest. Even small indoor gatherings like holiday dinners with family have experts worried. Until we have herd immunity to the virus—which isn’t even guaranteed with the vaccines, depending on how they work—gathering so freely with others unfortunately needs to remain a thing of the past.
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