Explained: How ZyCov-D vaccine works, how it is different

As Marc Andreessen highlights in his essay, vaccine technology – the unprecedented pace at which it was developed and made available widely has to go down as the biggest testimony for humanity’s technological prowess in recent times. Especially, the mRNA technology which holds so much promise beyond just the Covid vaccine in terms of solving critical medical issues. Now, there is news of another Nucleic acid based vaccine technology seeking approval – this time DNA based. Indian pharmaceutical company Zydus Cadila has applied to the Indian drug regulator for emergency use authorisation of its Covid vaccine – ZyCov-D, which if approved will become the world’s first DNA vaccine against Covid according to this piece in the Indian Express. This article helps us understand the technology in simple terms and compares and contrasts with other vaccines in the market.
“ZyCov-D is a “plasmid DNA” vaccine — or a vaccine that uses a genetically engineered, non-replicating version of a type of DNA molecule known as a ‘plasmid’.
The plasmids in this case are coded with the instructions to make the spike protein of SARS-CoV-2, the coronavirus that causes Covid-19. Vaccination gives the code to cells in the recipient’s body, so they can begin making the spiky outer layer of the virus. The immune system is expected to recognize this as a threat and develop antibodies in response.
Most Covid-19 vaccines currently are given in two doses, with a couple of single-shot ones also available. ZyCov-D by contrast, will be given in three doses, with an interval of 28 days between the first and second and second and third shots.
 The other unique thing about the vaccine is the way it is given. No needle is used — instead, a spring-powered device delivers the shot as a narrow, precise stream of fluid that penetrates the skin.”
With the spread of Delta variant across the world, there are concerns about the efficacy of the incumbent vaccines. Cadila claims ZyCov-D is effective against Delta.
“The large-scale phase 3 trial of ZyCov-D was conducted at 50 clinical trial sites across the country “during the peak of the second wave of Covid-19”, and the company believes that this “reaffirms” the vaccine’s effectiveness against the Delta variant of the coronavirus.
“You know that 99 per cent of all strains that have been found in sero (surveillance) tests have been the Delta variant… Our data was in the peak of April, May, and June,” Dr Patel said.
He said the company can “upgrade” ZyCov-D “if needed” to target other variants of concern and variants of interest that become more infectious or virulent in nature. The company is currently “making the constructs” to study the current effectiveness of the vaccine in neutralizing these variants.”