A single case appears to have been responsible for many of the other eventual cases, the team at the Broad Institute in Massachusetts reported.
One was especially bad. A virus that carried a mutation, a small genetic change that they labeled C2416T, was apparently brought to the conference by just one person and ended up infecting 245,000 people. A subset of the viral strain with a mutation known as G26233T ended up in 88,000 of these cases.
“A single introduction had a massive effect on subsequent transmission because it was amplified by spreading in a very mobile population very early in the outbreak, before many public health precautions were implemented,” the team wrote.
“While Massachusetts accounted for most of the conference-related early spread, Florida accounted for the highest proportion of cases overall,” they added.
It is difficult to document a super-propagation event. Researchers must show that the people were infected and in contact with each other. When tens of thousands or hundreds of thousands of people are involved, it is almost impossible.
But the genetic fingerprint makes it possible. Broad’s team used databases of the virus to track these individual changes, known as single nucleotide polymorphisms, or SNPs (pronounced “snips”).
“We believe this is an important warning about the subsequent implications of over-propagation, which is even more relevant as we enter the peak of the holiday season and begin to implement vaccines that may not decrease transmission,” MacInnis told CNN.
Only about 200 people attended the Biogen conference in Boston in late February, held before precautions against a widespread pandemic were implemented. Since then, the company has collaborated with researchers to help study what happened.
The C2416T mutation may have originated outside the US Researchers checked 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 before March.
“Taken together, this strongly suggests 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 superpropagation at the conference.” , the researchers wrote.
In other words, a single person brought this particular version of the virus to Boston and it spread through the conference.
The second viral fingerprint, G26233T, appears to have emerged from the conference, the researchers said. “It is not seen anywhere else in the public genome databases prior to the cases associated with the conference,” they wrote.
These particular fingerprints are a handy way to track the spread of the virus from a single event.
The C2416T mutation spread rapidly in the Boston area, showing up in 30% to 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 coming from the first wave of the pandemic in the Boston area and we hope that the information gleaned from this data will help continue to drive a better understanding of the transmission of this virus. and efforts to address it, “Biogen said in a statement.