BOSTON — Analysis of the genomes of hundreds of COVID-19 virus samples connects the dots between a strain of the virus that was being transmitted in Europe and a so-called superspreading event in Massachusetts which led to cases throughout the Boston area, in other states and even in other countries.

The authors wrote that their results “highlight the failure of measures to prevent importation” of the virus early during the pandemic – such as with the international travelers who attended the Biogen leadership conference held in Boston in late February.

“Our findings repeatedly highlight the close relationships between seemingly disconnected groups and populations: viruses from international business travel seeded major outbreaks among individuals experiencing homelessness, spread throughout the Boston area, and were exported to other domestic and international sites,” researchers wrote.

The research was published Tuesday by a preprint service for health sciences and has not yet been peer reviewed. The work is credited to numerous authors, including researchers from the Broad Institute and Massachusetts General Hospital. Sponsors of the work include the National Institute of Allergy and Infectious Diseases, the Centers for Disease Control and Prevention, the US Food and Drug Administration and several other government and charitable organizations.

According to the report, the analysis included “nearly all confirmed early cases of the epidemic in (Massachusetts) through March 8.”

The researchers said they found genetic evidence of more than 80 times the virus was introduced into the Boston area.

Through one specific genetic variation, researchers said they linked numerous cases to an international business meeting held in Boston.

While researchers did not identify the meeting by name, they did reference it as being held on Feb. 26 and 27, which matches the dates of the Biogen leadership conference held at the Marriott Long Wharf. It was attended by about 175 employees, including some from Europe.

Researchers wrote that samples from cases known to be linked to that conference were linked to a genetic marker, identified as C2416T, which was being spread in Europe during February.

“The signature of superspreading can indeed be seen in the conference-associated cases,” the authors wrote.

"February 2020 was nearly a half year ago, and was a period when general knowledge about the coronavirus was limited. We were adhering closely to the prevailing official guidelines. We never would have knowingly put anyone at risk," Biogen officials wrote in a statement Tuesday.

Of the 744 Boston-area cases analyzed for this study, more than 35% were linked to this one genetic marker. The marker also subsequently appeared in samples from other states and countries, the authors wrote.

The authors wrote that the Biogen event likely had “an outsized effect because it occurred early in the pandemic.”

“This, along with epidemiological data connecting multiple conference-linked cases to other U.S. states, suggests that most C2416T viruses in the U.S. likely derive from this initial introduction,” the report states. “However, we cannot estimate the absolute number of individuals involved as sequenced genomes are not a random sample of cases and U.S. state-level data is highly incomplete at this time.”

The researchers also concluded that at least two of the seven introductions of COVID-19 to guests and staff of the Boston Health Care for the Homeless Program carried genetic markers related to the samples from the Biogen conference. Those mutations were eventually found in more than half of the samples analyzed from cases at that shelter.

Authors also analyzed another superspreading event in a skilled nursing facility. In that example, 75 of the 83 examined viral genomes were determined to be closely related.

A key difference between that superspreading event and the Biogen conference, they wrote, is that the spread was more contained.

“While devastating to the residents, (it) had little large-scale effect because it occurred later and in a more isolated population,” the authors wrote.

Full statement from Biogen:

"When we announced our collaboration with the Broad Institute of MIT and Harvard in April, we explained that the COVID-19 pandemic had a very direct and personal impact on the Biogen community, and many colleagues were eager to help others through the pandemic by sharing de-identified biological and medical data to advance knowledge and the search for potential vaccines and treatments.

"February 2020 was nearly a half year ago, and was a period when general knowledge about the coronavirus was limited. We were adhering closely to the prevailing official guidelines. We never would have knowingly put anyone at risk. When we learned a number of our colleagues were ill, we did not know the cause was COVID-19, but we immediately notified public health authorities and took steps to limit the spread

"With more than 5.7 million US confirmed cases and 23.6 million confirmed global cases today, there is a much greater understanding of how easily and quickly this virus can be transmitted, and we are proud to contribute through this scientific collaboration to the global effort to overcome COVID-19."