What is screening?
Screening is a test which is positive only if it is in contact with the variant that is sought. Quebec scientists must therefore develop a test that reacts only to specific mutations of the Omicron variant.
“It’s the game of seven differences. We take the genetic sequence of Omicron, we compare it to the genetic sequence of Delta, which circulates mainly in Quebec, and we look for the mutations that are present in Omicron, but which are not present in Delta, ”explains Mr.me Moreira.
The wonderful thing about this creepy variant is that it has so many mutations that it’s easy to find differences with Delta.
Sandrine Moreira, from the Quebec Public Health Laboratory
If the test is positive, the health authorities will perform a complete sequencing to confirm that it is indeed the Omicron variant, confirmed the Minister of Health and Social Services, Christian Dubé, at a press conference in Montreal, Monday.
What is the difference between screening and sequencing?
Sequencing is the most efficient method for identifying new variants of concern, since it allows the complete genetics of a virus to be analyzed. However, it is a long and expensive process which can only be carried out on a fraction of the positive cases.
“Sequencing is the extreme version of screening. We will not only be interested in the variants that we already know, we are looking at all the mutations, ”says the specialist.
Indeed, the screening does not make it possible to identify new variants. It is absolutely necessary to do sequencing to see the evolution of the virus, its mutations and the new variants.
The national director of public health, Dr Horacio Arruda, recalled Monday that Quebec was currently sequencing “randomly” among positive cases.
What are the advantages of screening?
Screening is an inexpensive method. “A sequenced sample costs between $ 75 and $ 100 per sample. Screening is about twenty dollars, so it’s much lower, ”says M.me Moreira.
Screening also allows results to be obtained much faster.
The screening takes about 30 minutes to prepare for a batch of 80 tests, and one has a result in one hour. So, a sample that arrives at 10 am, we can have the result at noon.
Sandrine Moreira, from the Quebec Public Health Laboratory
However, it takes more than a week to obtain the result of a sequencing. “It takes several days to prepare the sample, then it takes at least a day [pour séquencer le virus] and at least one day of computer analysis. In total, it takes about a week and sometimes more ”, explains Mme Moreira.
Why had Quebec stopped screening?
In recent days, the page monitoring the circulation of variants of the National Institute of Public Health of Quebec (INSPQ) was no longer updated on a daily basis.
On the organization’s website, it is explained in particular that screening is no longer carried out “because of the marked dominance” of the Delta variant. But the arrival of the Omicron variant will revive these activities.
“There, now that we know there is a new variant, all travelers and people returning from outside are going to be screened. And if the screening is suspect, we will sequence them. There will also be systematic screening which will be done on certain days to assess whether there is no internal transmission ”, indicated the Dr Arruda.
Can samples that are several weeks old be screened or sequenced to find out if a new variant has been in Quebec for a long time?
“Certainly,” says Mme Moreira. In Quebec, all of our sequenceable positive samples, that is to say samples that have a fairly high viral load, are stored in a biobank. A huge majority of positive samples from Quebec are there, so we can go back and re-sequence samples. The specialist specifies that this procedure has occurred several times since the start of the pandemic.