The team analyzed 2,921 gene sequences for SARS-CoV-2 sequencing in Quebec. (New window) Collected from victims during the first wave. These sequences are an essential tool for tracking the local and global spread and evolution of the virus and its variants.
From one infection to another, pathogens naturally accumulate mutations in their genes. These errors can be used as markers for transmission because genes with similar sequences are linked. It allows researchers to establish a relationship between viruses (phylogeny) and establish where the virus comes from and how it is spread.
It’s like reading bar codes [pour chaque infection]
Says Jesse Shapiro, one of the authors of the study and an associate professor at the Genome Center at McGill University.
“Founding effect”
Of the 2,921 gene sequences analyzed in several individuals, the researchers estimate that 600 cubic meters were introduced for the spring break (from February 29 to March 9, 2020) and two weeks after the border was closed until March 31, 2020. One week after the installation of passenger isolation.
However, most of these cases did not result in large-scale transmission and show analyzed gene sequences. In addition, the repatriation of Canadians did not generate large-scale transactions in Quebec (less than 50 views analyzed).
There are many infections that go nowhere, and the mutations in those infections will go away. It may be that the person went into isolation or was able to control the spread.
, Transparent m. Shapiro.
In contrast, the analysis shows that the viruses introduced in Quebec before the spring break had the greatest impact on the spread of the disease in the province.
I will not criticize the spring break [pour le début de la propagation au Québec]. These were the first infections that led to a large number of infections.
The first case of COVID-19 in Quebec was confirmed on February 25, 2020, but, according to analysis, it is estimated that there were 15 to 17 virus outbreaks in the province before February 25; Most of them are unrelated to travel history.
These early introductions have proven to be difficult to eliminate, a phenomenon that has been seen around the world. In fact, these were the first events that triggered the spread in Quebec.
Following the event, Mr. Shapiro explainsEstablishment effect
, The first lines of a virus reach a place where it spreads most successfully. Those who come later are generally less likely to find their way.
Thus, most of the virus lines brought in from abroad disappeared soon after their introduction in Quebec. This is a little lucky game; Viruses that come first are the first to spread and have the best chance of establishing themselves.
Jesse Shapiro is one of the authors of the study.
Photo: Radio-Canada
Effect Super-propagandist
Of the more than 600 virus introductions in Quebec, 52 to 63% led to less than 20 cases. On the other hand, 7 to 12 introductions (0.9 to 1.6%) would have caused approximately 1000 cases. Thus, minority infections led to dozens or hundreds of subsequent infections. These lines were well established in Quebec and were still in the population in May.
These results show that there was an event of super-propaganda in Quebec, as seen elsewhere in the world, especially in Massachusetts and the United Kingdom.
The first viruses led to large chains of spread
, Dit M. Shapiro.
The most contagious genetic development coming from Europe
The researchers were able to establish that most of the lines analyzed came from Europe.
Of the 2921 queues analyzed, with the help of public health officials’ investigations, 328 were able to confirm that they had recently traveled. Most travelers reported returning from the Caribbean and Latin America (32%), mainly Mexico (9.5%) and the Dominican Republic (9%).
The same proportion came from Europe, mostly France (12%) and Spain (6%). Finally, 24% came from the United States.
Less than 1.5% of travelers returned from Asia and no one went to China, the epicenter of the epidemic.
The D614G mutation in spike protein – the mutation of the original Wuhan mutation first seen in Europe – was one of the ten most widely introduced viruses in Quebec.
In contrast, analyzes show that the first infections in western Canada and the United States came mostly from China.
According to Shapiro, the fact that the virus is already spreading around the world shows that closing the borders (only for travelers returning from China in the first place) is not enough.
We were catching on at the time. Even before we had conclusive evidence, the virus had already spread a lot [dans le monde]. Isolation for passengers was effective, but if it had been placed earlier it might have broken some diffusion chains.
