What Are DNA Vaccines?

ZyCoV-D. India hopes that a new approach to vaccination will give it a better shot at tackling covid-19. On August 20th the country’s drug r...

ZyCoV-D.

India hopes that a new approach to vaccination will give it a better shot at tackling covid-19. On August 20th the country’s drug regulator granted emergency-use approval for ZyCoV-D⁠—the world’s first DNA vaccine to be authorized for humans. Zydus Cadila, the vaccine’s developer, said it plans to make up to 120m doses annually, with the first licensed shots expected to be given next month. 

DNA vaccines could play a part in fighting other illnesses such as cancer and HIV, too. So how do they work, and how different are DNA vaccines from others already on the market? Conventional vaccines work by turning a virus against itself. 

A significantly weakened or inactivated form of the virus is injected into the body, training the immune system to act rapidly against the live virus, should it attack. But growing large amounts of a virus and weakening or extracting parts of it can be fiddly and laborious, especially if it keeps mutating. 

Medical scientist of Zydus Cadila.

Starting in the late 20th century, scientists tried to devise a simpler way of teaching the body to fight off an illness. This led to a new generation of immunisation: genetic vaccines. Most of these being used against covid-19, such as the vaccines developed by Pfizer and Moderna, use messenger ribonucleic acid (mRNA), a molecule that carries instructions for how to make a protein from a cell’s DNA in the nucleus to the molecular factories. 

But DNA vaccines, such as ZyCoV-D, begin one step back in the process. Developers start by finding DNA that will develop the spike protein (the part of the virus that helps it bind to its host) and carry it into the cell. The DNA is then transcribed into mRNA which instructs the cell to make the target viral protein, priming the immune system.

Both DNA and mRNA vaccines have robust safety records and far lower production costs than conventional ones. They can also be easily adapted to deal with mutations of the virus. But DNA vaccines have an advantage over their mRNA counterparts. They are more convenient to transport and store, making them much easier to distribute in poor countries with weak infrastructure. ZyCoV-D is stored between 2°C and 8°C but has shown good stability at temperatures of 25°C for at least three months. Pfizer’s, however, is stored at temperatures as low as -80°C. 

Interim results from a phase III clinical trial in India showed the ZyCoV-D vaccine was 66.6% effective at preventing symptomatic cases. That is lower than some other covid-19 vaccines, such as Pfizer's, when tested against the Delta variant, but still offers useful protection. ZyCoV-D’s approval comes as some countries have struggled to secure enough doses of covid-19 vaccines. 

DNA vaccines have unlocked yet another class of vaccination to experiment with in the fight against covid-19 and other illnesses. More could soon come to market. Inovio, an American biotech company, has its own vaccine in late-stage trials, as does Osaka University with AnGes and Takara Bio, two Japanese companies. And genetic vaccines are being touted as potential treatments for other illnesses such as cancer, where the vaccines would turbocharge the immune system by delivering genetic information that teaches it to recognise tumour antigens. 

An mRNA vaccine designed to combat HIV will start trials soon. The pandemic has fast-tracked these innovative methods of vaccination that previously lacked the resources to get into people’s arms. Their funding could now have implications for other diseases, long after covid-19 ceases to be a grave threat.