The United States had its first coronavirus superspreader event during a two-day conference in Boston organized by the biotech company Biogen in February. Genetic testing has revealed that what began with 99 people who became infected with SARS-CoV-2 at the event, another 205,000–300,000 cases subsequently resulted as the attendees returned home to 29 states and several other countries, carrying the virus with them, according to a study published in Science on December 10.

A national database of SARS-CoV-2 genomes and contact tracing has allowed the authors to track which strains were being transmitted. As The Boston Globe reports, the proportion of the pandemic attributed to the conference is roughly 1.6 percent of all US COVID-19 cases.

By performing genetic analyses from 28 of the infected conference-goers, researchers were able to identify the viral strain that circulated among them and that then spread around the country....

The conference was held February 26 and 27, weeks before any state declared stay-at-home orders or other measures to curb COVID-19 transmission. According to the Massachusetts Department of Public Health, there were only three presumptive cases in the first week of March and the state’s Public Health Commissioner Monica Bharel said at the time that there was low risk in Massachusetts.

“It’s a cautionary tale,” Bronwyn MacInnis, a genomic epidemiologist at the Broad Institute of Harvard and MIT and a coauthor of the paper, tells The New York Times. “When we hear these stories of clusters where 20 or 50 or 100 were affected, that does not account for what happens after.”

Soon after the cluster of cases was tied to the event in the spring, Biogen partnered with the Broad Institute to create a biobank to learn as much as possible about COVID-19 through blood samples from Biogen employees and their close contacts. The company has maintained a presence in COVID-19 research.

See “Biogen Uses its Own Superspreader Event to Aid COVID-19 Research

“Tremendous progress has been made since the start of the pandemic to gain a better understanding of this novel virus and its transmission, develop vaccines, and investigate potential treatment options,” reads a Biogen statement to the Globe, following the publication of the study. “As a company rooted in science, we understand the value of the data that came from the first wave of the pandemic in the Boston area and we hope that information gleaned from these data will help continue to drive a better understanding of the transmission of this virus and efforts to address it.”

The authors expressed in various news reports that while the strain is unique, it isn’t more virulent than others.

“The conditions that allow these super-spreading events to occur are very much still with us and will continue to be with us for a long time,” lead author Jacob Lemieux of the Broad Institute tells the Times, warning about the upcoming holidays. “Maintain social distancing, wear masks whenever possible and avoid indoor gatherings.”

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