A lab technician with blood samples from volunteers at the Moderna vaccine candidate clinical trials in Miami on September 2.
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Taimy Alvarez / AP / SIPA
The United Kingdom gave the green light on Wednesday to the vaccine developed by Pifizer and BioNTech.
Just like the one under development by the Moderna laboratory, it uses messenger RNA.
Etienne Decroly, research director at CNRS, and Nicolas Leulliot, professor of biophysics at the University of Paris, explain how this new vaccination technique works.
They rule out the fear of seeing a "modification" in the DNA of the person vaccinated with this technique.
The first British patients should be vaccinated as early as next week.
The United Kingdom announced on Wednesday that it had authorized the Pfizer / BioNTech vaccine against the coronavirus.
This vaccine, like that of its competitor Moderna, which has also announced high efficacy - without however having yet submitted the data to a scientific publication - uses a technology that has hitherto been unprecedented in humans.
Instead of an injection of an inactivated or attenuated virus, the teams of these two consortia bet on messenger RNA.
This new technique has given rise to fears, in particular that of a risk of "modification" of the DNA of vaccinated people.
We disentangle the truth from the false with two scientists, Etienne Decroly, research director at the CNRS, and Nicolas Leulliot, professor of biophysics at the University of Paris and specialist in RNA structures.
Messenger RNA, a molecule used to produce proteins
"Messenger RNA is a biological molecule that will be used by the cellular translation machinery, called ribosomes, to produce proteins," explains Etienne Decroly.
“In a cell, genetic information is contained within DNA, but DNA is not the messenger of information,” he adds.
In order for the information in DNA to be translated into protein, cells synthesize RNA molecules.
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There are several types of RNA.
Messenger RNAs, also known as mRNAs, can be recognized by modifications at each end of the molecule.
How does vaccination work with this new technology?
"The idea of the mRNA vaccine, as in any vaccine, is to present to the immune system a protein of the virus, which we may encounter during an infection, to 'train' the immune system to recognize and destroy the intruder, ”explains Nicolas Leulliot.
“Conventional technology is to use attenuated or deactivated viruses, which allows the immune system to be trained without having the adverse effect of the virus,” he adds.
The difference, with the mRNA vaccine, is that we will not inject a protein, but an mRNA.
It is through the latter that our immune system will react to the vaccination.
The mRNA, by entering our cells, will allow the production of the virus protein.
It is therefore "our cells which will produce the virus protein, as is the case when the virus infects us", adds the scientist.
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Do not confuse DNA and RNA
On paper, this technology is "fairly safe", advances Etienne Decroly.
And we must not confuse RNA and DNA.
“What should be noted is that it is RNA, not DNA that is used.
RNAs are molecules which by nature are more unstable than DNA.
These vaccines contain only the RNA which codes for a single protein of the virus, the S protein, which forms the crown giving the name to these viruses.
There is no possibility that an infectious virus will be produced from this vaccine.
The pieces of the virus machinery are missing that allow the virus to replicate.
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The two scientists rule out the possibility of DNA modification by this vaccination technique.
There are no “primers” that would make it possible to do this, explains Etienne Decroly: “RNAs are not used in cells to reproduce DNA.
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Even though DNA can be synthesized from RNA, thanks to certain enzymes, this will not be the case with this vaccination process.
“These enzymes are not normally produced by cells and, moreover, these enzymes are unable to initiate DNA synthesis in the absence of primers.
Here there are no primers.
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"We do not touch the genome"
With this vaccine, "we do not touch the genome," says Nicolas Leulliot.
“We will simply provide a photocopy of a gene, in the form of RNA.
This photocopy is not intended to modify our genome.
We are not going to become genetically modified beings.
Fortunately, this cannot happen, because otherwise it could also be the case when the virus infects our cells….
There will be in our cells the expression of a protein which is not ours, but in a transient way because the mRNA has a short time of life.
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Before being usable, this technology required numerous developments, in particular because of the fragility of RNA.
Nicolas Leulliot cites other obstacles that had to be overcome: “When this RNA arrives, it must be recognized that the translation machinery can take charge of it, produce the protein, that this protein is well folded, etc.
But it is also necessary to avoid that the RNA is not identified as a "foreign" RNA - which does not belong to our genome -, because this can trigger its degradation or an immune reaction against the mRNA.
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Vaccines, "our best allies in the fight against infectious diseases"
There are still unknowns around these vaccines: the level of protection for the elderly, or the type of immunity offered (will vaccinated people no longer be contaminated by the coronavirus).
"Another question that cannot be answered is how vaccines will induce selection pressure on the virus and therefore allow - or not allow - the development of viruses that would be less sensitive to vaccines", Etienne analyzes Decroly.
The researcher would like to point out that “vaccines have so far been our best allies in the fight against infectious diseases.
There have nevertheless been several resounding successes linked to vaccination: the vaccine against smallpox, which allowed its eradication, when it was an extremely serious disease, and the vaccine against measles, which is very effective.
[…] We are in Europe in a situation where we no longer see the benefits of vaccines because we no longer see the effects of infectious diseases.
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