A business conference held in Boston in late February may have led to around 20,000 COVID-19 cases, after attendees unknowingly spread the virus.
The event, a conference for biotech firm Biogen held between Feb. 26-27, included about 200 international attendees, including some from Italy, where the northern regions had just shut down to contain an outbreak of COVID-19.
With just 15 reported cases in the U.S. at the time, the attendees shook hands, shared buffet food and kissed each other on the cheeks, The Washington Post reported, unaware that COVID-19 was already circulating amongst them. Once the conference ended, guests returned to homes in Massachusetts, North Carolina, Indiana and abroad, including Australia, Singapore and Slovakia.
Just among the attendees and their close contacts, more than 90 people were diagnosed with COVID-19, “raising suspicion that a superspreading event had occurred there,” according to a new study.
The high rate of transmission out of this single conference led 54 researchers from hospitals and institutions across Boston to sequence and analyze the strain of the virus found in the infected attendees, and compare that to the ones that circulated in the Boston area. They found that the conference strain of COVID-19 matched that of hundreds of people in the region, along with people as far as Alaska, Luxembourg and Senegal.
The strain was also the same type found in about one-third of all COVID-19 cases sequenced in Massachusetts as of mid-July, indicating that the conference led to immense community spread.
Just a month after the conference, more than 600 residents and staff at one of Boston’s largest homeless shelters were tested for COVID-19 as a safety precaution. Health officials were stunned to find that 230 people had already been infected, and genetic sequencing for this study determined that nearly two-thirds of the cases from the shelter were the same strain from the Biogen conference.
“Our jaws dropped,” said Dr. Pardis Sabeti, a computational biologist at the Broad Institute and one of the lead researchers on the study told the Post. “It was the realization that these events really affect the most vulnerable among us.”
The researchers say that the conference was a “perfect storm” of factors, from the international group to the close contact among attendees, to create a superspreader event.
“That the virus was introduced at the conference at all was unlucky," Dr. Bronwyn MacInnis, a researcher at the Broad Institute who worked on the study, told CNN. "When it happened was critical: it was scheduled just as we were collectively beginning to appreciate the imminent threat of COVID at home — if it had been a week later the event likely would have been cancelled.”
MacInnis noted that the conference occurred before COVID-19 testing was available in the U.S., before social distancing was understood and well before the Centers for Disease Control recommended masks.
Based on the spread of the virus among attendees and the lack of COVID-19 restrictions at the time, the researchers estimate that this conference led to 20,000 infections.
“This is not a rigorous estimate but does communicate the scale,” MacInnis said. “If tens of thousands of individuals seems large, it is important to point out that it is in context of a pandemic that has infected tens of millions of people.”
The conference and the cases that followed should serve as a lesson on how swiftly COVID-19 can spread, the researchers said.
“We didn’t know better,” said Jacob Lemieux, a physician and infectious-disease expert at Massachusetts General Hospital and lead author of the study told the Post. “The difference now is there is increasing scientific evidence to show what can happen from a single event like that. We do know better. So we need to learn the lesson.”
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