India is preparing to fight Covid-19 with the world's first DNA vaccine for humans.

ZyCoV-D, the distribution of which was urgently authorized by Indian health authorities on August 20, is due to begin to be administered to the population in September.

A vaccination campaign that will be closely followed, as DNA vaccine technology is, like those with messenger RNA from Pfizer or Moderna, considered as a hope for treating or protecting against a wide range of serious diseases.

66% effective

ZyCoV-D strengthens the country's vaccine arsenal - in addition to AstraZeneca, Indian Covaxin and Russian Sputnik V - at a time when India begins to see the end of a catastrophic year in terms of health .

The number of new cases has risen to around 40,000 per day from more than 400,000 new infections daily in May, and the number of deaths has also been divided by ten from the peak of the epidemic.

The devastation of the second wave of Covid-19 in India, due in part to the famous Delta variant that emerged there, has prompted New Delhi to allocate as many resources as possible to the development of local vaccines.

And ZyCoV-D is the main illustration of this.

It has been shown to be 66% effective in protecting against serious forms of Covid-19, announced the Indian pharmaceutical group Cadila Healthcare in the press release presenting the results of its clinical trials carried out on 28,000 participants since January. A rate that seems modest compared to the more than 90% effectiveness of messenger RNA vaccines from Pfizer or Moderna. However, ZyCoV-D was tested while the Delta variant was rampant, while other vaccines were developed when only the original strain of Sars-CoV-2, less resistant to vaccine treatments, was still being discussed. recalls the pharmaceutical group.

Nevertheless, this first DNA vaccine will not escape comparison with its messenger RNA cousins ​​since "it is to them that it is the closest in its functioning", underlines Al Edwards, immunologist and specialist. vaccines at the University of Reading (England), contacted by France 24.

>> To read also: "Messenger RNA, the innovative technology behind the vaccines of Pfizer and Moderna"

These two families of vaccines use, respectively, a piece of RNA or synthetic DNA that contains "instructions for the body to make the famous Spike protein of the Sars-CoV-2 virus so that the immune system can develop antibodies. ", explains Pierre Saliou, associate professor of Val-de-Grâce and specialist in vaccinology, contacted by France 24.

More affordable and easier to store

The big difference is that the piece of synthetic DNA must be injected "deep in the cell nucleus in order to be able to be decoded while the messenger RNA can remain on the surface of the cell", summarizes Al Edwards.

The road ahead is therefore longer and more complicated, and this is the main reason why no DNA vaccine has been shown to be effective in humans so far.

Several have, however, been developed for animals, including a vaccine that protects horses against West Nile virus.

ZyCoV-D also needs to be administered three times, unlike most other vaccines, which are expected to be fully effective after a maximum of two injections.

DNA vaccines thus appear to be more complex to develop while offering potentially poorer protection against Covid-19 than messenger RNA vaccines.

So why not focus on the latter?

There are, in fact, still eleven other DNA vaccines under development, according to the list established by the World Health Organization (WHO).

First, betting on DNA seemed more promising.

"About a year and a half to two years ago [that is to say at the start of the pandemic], we weren't even sure that messenger RNA vaccines could work, while the laboratory work carried out for at least twenty years have demonstrated the feasibility of DNA vaccines, "said Al Edwards of the University of Reading.

ZyCoV-D et al. Also pose a much smaller logistical challenge than that of messenger RNA vaccines.

They can be stored for several months at temperatures between -2 ° C and 8 ° C, while messenger RNA vaccines should be placed in freezers at much lower temperatures.

"This is because DNA is extremely stable, whereas RNA strands are particularly fragile," explains Pierre Saliou.

Which also makes them, potentially, cheaper.

"No need to pay for specific storage solutions," says Al Edwards.

Easier to transport and store, and cheaper to deploy: these vaccines could be an ideal solution for developing countries.

In addition, a small bonus for belonephobes (those who are afraid of needles), ZyCoV-D does not require a prick since it is administered through a needleless injection system.

Where is the science?

These DNA vaccines share a central quality with those with RNA which makes part of the scientific community say that these are the vaccine technologies of the future: they are very adaptable.

The same technological platform that made it possible to develop the first DNA vaccine against Covid-19 can now be used to develop molecules to fight other ailments.

Such vaccines are also currently being tested against the Zika virus (disease transmitted by mosquito bite), or against HIV.

But it may still be a bit early to claim victory.

ZyCoV-D certainly seems to have convinced the Indian health authorities, but scientists would like to know why.

The Cadila Healthcare laboratory has not published specific data to scientifically corroborate the claims contained in the press release.

"ZyCoV-D is potentially a very good vaccine, but the lack of transparency is worrying," writes Jammi Nagaraj Rao, an Indian immunologist, in a column published by Indian news site The Wire.

“Indian biotech companies have the know-how to achieve medical breakthroughs of the caliber of a first DNA vaccine, but it is clear that having access to complete scientific data would be more reassuring,” admits Al Edwards.

This is why the continuation of the vaccination campaign in India - where only 17% of the population is fully vaccinated - will be followed very closely.

This will be the first full-scale test for a whole new family of vaccines.

For Al Edwards, "we must never forget that before the appearance of this virus, there was a lack of vaccine tools, and this pandemic has made it possible to prove the medical validity of innovative technologies" and which could make a difference beyond of the Sars-CoV-2 pandemic.

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