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Broad Institute researchers identified a conference held by the Cambridge-based company Biogen in February as a “superspreading” event for COVID-19 that caused tens of thousands subsequent cases in the Boston area.
The study, which tracked occurrences of unique COVID-19 genomes from a dataset of the earliest known cases of the virus in Massachusetts, was led by researchers from the Broad Institute and various universities. The team used viral genome sequencing – a process of decoding the nucleotides within a given genome – to find over 80 separate introductions of COVID-19 into Massachusetts.
The team marked the Biogen conference as a COVID-19 superspreading event after discovering that a specific variation of the virus containing the C2416T allele had contributed to 35.1 percent of COVID-19 cases studied in the dataset. Using the frequency of the allele in four Massachusetts counties, the study estimated that around 20,000 cases in the counties could be attributed to the event.
Samples from the Boston Health Care for the Homeless Program also revealed that the COVID-19 variation introduced at the conference spread into Boston homeless shelters.
In a statement provided by a Broad spokesperson, Broad scientists Bronwyn MacInnis and Stephen Schaffner – members of the team – wrote that the event most likely led to even more COVID-19 cases outside the Boston area.
“This back-of-the-envelope calculation does not include other counties in MA or any other US states or any other countries,” they wrote. “It thus seems likely that this is an event whose impact is measured in tens of thousands of individuals, but a precise estimate of the total number involved is not possible with current data.”
The study also found that effective isolation processes had resulted in lower rates of COVID-19 spread. Schaffner wrote in a Broad website post that a skilled nursing facility studied by the group had a lesser impact on the general Massachusetts population than the Biogen conference.
“The outbreak in the nursing facility was devastating for those involved, but it occurred in a fairly isolated population,” Schaffner wrote. “As a result, it caused little transmission outside the facility. The outbreak in the conference, by contrast, occurred in a highly mobile population in late February and spilled out into the larger community.”
Although the study accounted for almost all early confirmed COVID-19 cases, Lydia A. Krasilnikova, a Harvard graduate student and member of the team, wrote in an emailed that asymptomatic cases were “not a focus of this study.”
“It is entirely possible that there were additional asymptomatic cases in Massachusetts, even in the Boston area, that were not captured in our sampling—indeed, I would be very surprised if we captured all cases from early in the Massachusetts outbreak,” she wrote.
Krasilnikova wrote that the team plans to continue its collaborations with the Massachusetts Department of Public Health and Massachusetts General Hospital while continuing to use genomic sequencing to better understand the virus.
“Genomic epidemiology, especially combined with traditional epidemiology, can show us if cases or clusters of cases are connected: this can, with enough sampling, determine whether disease is being continually reintroduced into a community or is spreading within it,” she wrote. “These scenarios require different responses; genomic epidemiology can equip leaders with the information they need to make difficult and urgent decisions.”
—Staff writer Ethan Lee can be reached at ethan.lee@thecrimson.com.
