The team at the Broad Institute in Massachusetts reported that one case appears to have been responsible for another 245,000 final cases.
One of them was particularly bad. It appears that a virus carrying one mutation – a small genetic change identified as C2416T – was taken to the conference by one person, and it ended up infecting 245,000 people. A second viral strain with a mutation known as G26233T ended up in 88,000 people.
The team wrote: “One introduction had a significant impact on subsequent transmission because it was amplified by the super-spread in a highly mobile population very early in the outbreak, before many public health precautions were taken.”
They added, “While Massachusetts was responsible for most of the early deployments related to the conference, Florida accounted for the largest proportion of cases overall.”
It is difficult to document a widespread event. Researchers must demonstrate that people are infected and have been in contact with each other. When tens of thousands or hundreds of thousands of people participate, it is nearly impossible.
But genetic fingerprints make that possible. Broad’s team used virus databases to track these individual changes, known as single nucleotide polymorphisms or SNPs (pronounced “snippets).
“We think this is an important cautionary tale about the final effects of the super-spread, which is even more important as we enter the peak of the holiday season, and we start rolling out vaccines that may not reduce transmission,” McCaines told CNN.
Only about 200 people attended the Biogen conference in Boston in late February, which took place before the epidemiological precautions were taken on a large scale. The company has since collaborated with researchers to help study what happened.
The C2416T mutation may have originated outside of the United States. Researchers examined a global database of samples of the Coronavirus and found it in two French patients diagnosed on February 29. In the United States, it was only found in patients associated with the conference prior to March.
Taken together, the researchers wrote: “Taken together, this strongly indicates a low-level community transmission of C2416T in Europe in February 2020 before the allele (mutation) reached Boston via a single introduction, which was then amplified by the hyperpropagation at the conference.” .
In other words, one person carried this particular version of the virus to Boston and spread through the conference.
The researchers said the second viral fingerprint, G26233T, appears to have been born from the conference. “It did not appear anywhere else in any public genome databases prior to the cases associated with the conference,” they write.
These fingerprints are an easy way to track the spread of the virus from a single event.
The C2416T mutation has spread rapidly in the Boston area, appearing between 30% and 46% of samples taken in the four-county Boston area in early spring.
By November 1, 2020, viruses containing C2416T could be found in 29 states.
“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 hope that the information gleaned from this data will help in continuing to achieve a better understanding of this transmission,” Biogen said in a statement.