What are DNA vaccines?

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 authorised 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. 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.