Pfizer's Covid-19 vaccine is based on unproven technology - France 24

Washington (AFP)

Among the four major categories of vaccines developed against Covid-19, the one used by Pfizer, which announced Monday that its vaccine was 90% effective, had never yet been proven.

It is based on a new technology called messenger RNA.

All vaccines have the same goal: to train our immune system to recognize the coronavirus, to raise its defenses in a preventive way, in order to neutralize the real virus if it were to infect us.

Conventional vaccines can be made from inactivated (polio, influenza), attenuated (measles, yellow fever) viruses, or just proteins called antigens (hepatitis B).

But in the case of Pfizer and its German partner BioNTech, or Moderna, which uses the same technique but has not yet announced any results, strands of genetic instructions called messenger RNA are injected into the body, this is that is, the molecule that tells our cells what to make.

Every cell is a mini-factory of proteins, according to the genetic instructions contained in its nucleus.

The vaccine's messenger RNA is inserted and takes control of this machinery to manufacture a specific antigen of the coronavirus: the "spicule" of the coronavirus, its tip so recognizable which is on its surface and allows it to attach itself to human cells to penetrate them.

This spike, harmless in itself, will then be detected by the immune system which will produce antibodies, and these antibodies will stay, standing guard for, hopefully, a long time.

Once the genetic material is injected, "the cells which are at the site of the injection will start to produce, in a transient manner, one of the proteins of the virus, in this case the protein S, the spike protein", explained to AFP Christophe D'Enfert, Scientific Director of the Institut Pasteur.

- Accelerator -

The advantage is that with this method, there is no need to cultivate a pathogen in the laboratory, it is the organism that does the work.

It is for this reason that these vaccines are faster to develop.

No need for cells or chicken eggs (as with flu shots) to make this vaccine.

"RNA vaccines have the interesting feature of being able to be produced very easily in very large quantities", summarizes Daniel Floret, vice-president of the Technical Committee on Vaccinations, at the High Authority for Health.

Note that it is not possible for RNA to integrate into a human genome, made up of DNA.

"RNA, to be able to integrate into the genome, it has to be what is called reverse transcribed [in DNA] - we say retrotranscribed - and that does not happen spontaneously in the cells. ", explains Christophe D'Enfert.

As for the coronavirus protein, it "is not going to be produced all the time, it will stop" because, as with any vaccine, the immune system will destroy the cells that produce the viral protein.

"The process will therefore end by itself", explains Bruno Pitard (Inserm / University of Nantes), at the head of a start-up which is working on this type of vaccine.

The disadvantage of the latter: they must be stored at very low temperature.

The US government has been putting in place the necessary logistics for several months.

This is not the case with DNA vaccines, however, which can be stored at room temperature.

To date, no DNA or RNA vaccine has been approved for humans.

On the other hand, DNA vaccines exist for veterinary use: horses, dogs, salmon ...

The Covid-19 has given a huge boost, in particular thanks to public funding.

The US government, spurred on by President Donald Trump, signed a $ 1.95 billion contract with Pfizer to deliver 100 million doses, should the vaccine ever be approved.

Moderna, the smallest American biotechnology company, has been subsidized to the tune of $ 2.5 billion to develop the vaccine and produce 100 million doses.

All these doses will be delivered to the United States, which hopes to start immunizing vulnerable people before the end of the year.

If the technology is proven, this could pave the way for many other vaccines: Moderna has been developing messenger RNA vaccines for years against Zika, influenza, Epstein-Barr virus (mononucleosis), respiratory virus syncytial (bronchiolitis ...), cytomegalovirus (often not serious but can pose a risk in the fetus), but also against cancers.

© 2020 AFP