World's first DNA Covid vaccine ready for use

The world's first Covid-19 vaccine that uses circular strands of DNA to prime the immune system against the virus SARS-CoV-2 is ready to be rolled out in India.

ZyCoV-D, which is administered into the skin without an injection, has been found to be 67 per cent protective against symptomatic Covid-19 in clinical trials and will likely be administered in India by Oct 20.

Dr N.K. Arora, chairperson of the National Technical Advisory Group on Immunisation (NTAGI), told The Times of India that the vaccine is going through final quality checks at a laboratory in Himachal Pradesh.

"If everything goes as per plan, the vaccine will be introduced in the immunisation programme by October 15 to 20," he said.

Although ZyCoV-D's efficacy is not particularly high compared to that of many other Covid-19 vaccines, the fact that it is a DNA vaccine is significant, said researchers.

"It is proof of the principle that DNA vaccines work and can help in controlling the pandemic," Prof Peter Richmond, a paediatric immunologist at the University of Western Australia in Perth, told nature.com. "This is a really important step forward in the fight to defeat Covid-19 globally, because it demonstrates that we have another class of vaccines that we can use."

Close to a dozen DNA Covid vaccines are in clinical trials globally. DNA vaccines are also being developed for many other diseases.

"If DNA vaccines prove to be successful, this is really the future of vaccinology because they are easy to manufacture," said Dr Shahid Jameel, a virologist at the Ashoka University in Sonipat, Haryana.

Messenger RNA (mRNA) vaccines, such as Pfizer-BioNTech and Moderna, were quicker to show strong immune responses in clinical trials and have now been delivered to hundreds of millions of people around the world.

But DNA vaccines have a number of benefits, including being more stable than mRNA vaccines, which typically require storage at very low temperatures.

ZyCoV-D was developed by Indian pharmaceutical company Zydus Cadila, headquartered in Ahmedabad. On Aug 20, India's drug regulator authorised the vaccine for people aged 12 and older.

ZyCoV-D contains circular strands of DNA known as plasmids, which encode the spike protein of SARS-CoV-2, together with a promoter sequence for turning the gene on.

Once the plasmids enter the nuclei of cells, they are converted into mRNA, which travels to the main body of the cell, the cytoplasm, and is translated into the spike protein itself.

The body's immune system then mounts a response against the protein and produces tailored immune cells that can clear future infections. Plasmids typically degrade within weeks to months, but the immunity remains.

The challenge for DNA vaccines is that they need to make it all the way to the cell nucleus, unlike mRNA vaccines, which just need to get to the cytoplasm, said Dr Jameel.

So, for a long time, DNA vaccines struggled to induce potent immune responses in clinical trials, which is why they had been approved for use as vaccines only in animals, such as horses, until now.

To solve this problem, ZyCoV-D is deposited under the skin, as opposed to deep in muscle tissue. The area under the skin is rich in immune cells that gobble up foreign objects, such as vaccine particles, and process them.

"This helps capture the DNA far more efficiently than in the muscle," said Dr Jameel.

Unusually, the vaccine is delivered using a needle-free device pressed against the skin, which creates a fine, high-pressure stream of fluid that punctures the surface and is less painful than an injection.

But, despite being more potent than previous DNA vaccines, ZyCoV-D requires a minimum of three doses to achieve its initial efficacy.

This is likely to add to the logistical challenge of administering the vaccine during the current pandemic, said Dr Jameel.

Indo-Asian News Service

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