the race against time of researchers to unravel the secrets of this “worrying” mutation of the virus

Will their work calm the global panic? Since the detection, Thursday, November 25, of Omicron in South Africa, virologists and researchers in biology around the world are busy trying to unravel the secrets of this variant considered “worrying” by the World Health Organization (WHO). Initially called B.1.1.529, the Omicron variant worries specialists because of the presence of a large number of mutations which raise concerns about a significant transmissibility as well as a lower effectiveness of the current Covid-19 vaccines. How do scientists try to see more clearly about it?

Establish the virus profile

For the researchers, the first step is to comb through the sequence of the Omicron variant. Like a genetic identity card, this succession of letters determines all the characteristics of this new version of Covid-19. The Omicron sequence was put online by the South African laboratory that identified this variant on the Gisaid database, accessible to many researchers around the world.

“It is thanks to the sequence that we can determine the mutations and the profile of the virus”, summarizes Olivier Schwartz, director of the virus and immunity unit at the Institut Pasteur, and who is currently working on the subject in his laboratory which brings together around fifteen researchers.

“The sequence will make it possible to identify where the mutations are located: is it at places of contact with the ACE2 receptor, which serves as the entry point of the virus into our body? escape the antibodies? “

Olivier Schwartz, director of the virus unit at the Institut Pasteur

to franceinfo

It is by comparing the sequence of Omicron to that of the Delta and of the previous variants which circulated on the planet that the scientists were able to identify about thirty mutations in the Spike protein, which plays the role of key of entry of the virus. in the body. Some were present in known variants and others were not. Problem: the antibodies produced by the Covid-19 vaccines currently in use target the form of the Spike protein characteristic of the initial strain of Covid-19, identified in Wuhan, and could therefore be less effective against Omicron.

Synthesize part of the virus

Using Omicron’s genetic identity card, some labs can perform experiments even without having a virus sample on hand. “From sequencing, laboratories can synthesize genes and reintroduce them into their experimental systems”, explains virologist Etienne Decroly, CNRS research director, to franceinfo.

The Institut Pasteur is thus able to create, in about a week, cells producing a perfect replica of the Spike protein present on Omicron, dissociated from the virus itself. Researchers can then make benign viruses, called lentiviruses, produce this particular protein. “We use this to mimic the entry of Omicron into cells to observe the reaction of antibodies and to study, for example, the effectiveness of vaccines”, details Olivier Schwartz.

Observe the interactions of the virus

Laboratories with access to samples of the Omicron variant taken from patients can go further in the experiments by making the virus interact with serum. This liquid, obtained by centrifuging blood samples, is highly concentrated in antibodies, which makes it ideal for observing the body’s reaction to this new variant.

“The first thing the researchers will do is observe whether the antibodies produced by the body after a vaccination or a Covid-19 infection are effective in blocking the entry of Omicron into the cells”, explains Sandrine Sarrazin, Inserm researcher at the Marseille-Luminy Immunology Center.

Scientists from pharmaceutical laboratories producing vaccines against Covid-19 are working on this subject in particular, such as Pfizer, BioNTech and Moderna, details this specialist.

Thanks to the clinical trials still underway on vaccines, laboratories can observe the interaction of the new variants with the serum of patients who have received one, two or three doses and thus gauge the effectiveness of the antibodies depending on the situation.

Sandrine Sarrazin, researcher at the Marseille-Luminy Immunology Center

to franceinfo

It is with this same method that Pfizer, BioNTech and Moderna will test vaccine preparations suitable for Omicron, before launching any clinical trials. The first two said on Friday that they were “prepared several months ago to adjust their vaccine in less than six weeks and deliver the first doses in 100 days” whether a variant is found to be resistant to the antibodies produced by current vaccines.

In addition, tests can be performed on animals, such as mice genetically modified to add the ACE2 receptor to which Sars-CoV-2 binds to enter the body. Golden Syrian hamsters, known to be naturally sensitive to Covid-19 while developing moderate pathology, can also be used for in vivo experiments.

Examining the dynamics of the epidemic

Unfortunately, much of the study of the dangerousness of Omicron will be based on statistics from people directly infected with this variant. In order to gauge its transmissibility, and therefore its ability to supplant Delta or not in the dynamics of the epidemic, researchers will measure the evolution of the proportion of positive screenings linked to Omicron.

“Each positive PCR test reported in the government platform Sidep, if it has been the subject of a screening test, allows us to know if three mutations, called E484K, E484Q and L452R, were or not present in the detected virus. in the patient “, explains Florence Débarre, researcher in evolutionary biology at the CNRS.