India has approved a new COVID-19 vaccine that uses circular strands of DNA to prime the immune system against the virus SARS-CoV-2. Researchers have welcomed news of the first DNA vaccine for people to receive approval anywhere in the world, and say many other DNA vaccines might soon be hot on its heels.

ZyCoV-D, which is administered into the skin without an injection, has been found to be 67% protective against symptomatic COVID-19 in clinical trials, and will probably start to be administered in India this month. Although the efficacy is not particularly high compared to that of many other COVID-19 vaccines, the fact that it is a DNA vaccine is significant, say researchers.

It is proof of the principle that DNA vaccines work and can help in controlling the pandemic, says Peter Richmond, a paediatric immunologist at the University of Western Australia in Perth. “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 vaccines against COVID-19 are in clinical trials globally, and at least as many again are in earlier stages of development. 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, says Shahid Jameel, a virologist at Ashoka University in Sonipat, India.

ZyCoV-D was developed by Indian pharmaceutical firm Zydus Cadila, headquartered in Ahmedabad. On 20 August, India’s drug regulator authorized the vaccine for people aged 12 and older. The efficacy figure of 67% came from trials involving more than 28,000 participants, which saw 21 symptomatic cases of COVID-19 in the vaccinated group and 60 among people who received a placebo.

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.

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