We reported back in March 2020 about a Biogen conference held in Boston where three attendees tested positive for COVID-19. At the time, there was widespread concern about the impact this event would have on wider outbreaks within the state. Now, evidence shows that this event seeded thousands of COVID-19 infections across the United States and in countries as far away as Singapore and Australia.
Tracing back
The recent study, published as a preprint in medrxiv, provides an unprecedented look at how the virus opportunistically spread at these types of events. The results come from a project run at the Broad Institute of Harvard and M.I.T. that began in early March. The team sequenced and analysed the viral genomes of 7,772 individuals infected with COVID-19 between January and May 2020. They also performed phylogenetic analysis of the virus to trace where each virus emerged from.
The data revealed that the virus was introduced into the Boston area on 80 occasions. This was mainly from other areas in the United States and from Europe. The team investigated events, including the Biogen conference and congregate living environments (homeless shelters and nursing facilities), to determine whether they were superspreading.
The team found that 85% of residents and 37% of staff at a skilled nursing home were infected with SARS-CoV-2. The researchers identified three different viral lineages within the home. One of these accounted for 90% of the infections.
A single event
The dataset contained virus genomes from 28 attendees of the Boston conference. The team were able to identify a variant (C2416T) which clustered in all the genomes. The first reporting of this variant, before the event, was two French patients in February 2020. It was suggested that there was low level transmission of C2416T in Europe in February before the variant was then introduced into Boston and amplified by superspreading at the conference. The team note that there is strong evidence that a second variant – G25563T- emerged during or immediately after the conference. This was because researchers first detected the variant in 7/28 attendees. C2416T/G26233T subsequently spread into surrounding communities. Interestingly, the researchers found that 105 viral genomes within a Boston homeless shelter had the C2416T variant, and 54 had both C2416T/G26233T.
Dr Bronwyn MacInnis, researcher at the Broad Institute and co-author of the report, stated:
“We had no idea it would be associated with the conference. It came as a complete surprise.”
Although it is difficult to determine how many people acquired the virus in the months after the conference, the team estimate that approximately 20,000 cases may be connected to this one event.
This study demonstrates how the conference, like many other similar events, amplified and spread the virus in the early months of the pandemic. These types of superspreading events represent a hallmark of coronavirus. It is therefore important to remember that following guidelines and safety measures can be imperative because one bad decision can impact thousands of lives.
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