India's drugs regulator approved a coronavirus vaccine by Zydus Cadila for anyone aged 12 and above, clearing the first shot for use in children and adding a sixth inoculation in India's toolbox to fight the pandemic.

The approval was given by Central Drugs Standards Control Organisation (CDSCO) after its experts assessed results from the company's phase III clinical trials that showed the vaccine to have an efficacy of 66.6%. Officials said it can be rolled out to those under the age of 18 once the inoculation drive is officially expanded to cover children – at present, it is only for adults.

"India is fighting Covid-19 with full vigour. The approval for world's first DNA based 'ZyCov-D' vaccine of @ZydusUniverse is a testimony to the innovative zeal of India's scientists. A momentous feat indeed," Prime Minister Narendra Modi tweeted on Friday.

The company confirmed the approval and said it has already stockpiled doses. "…the company has received the emergency use authorisation… for ZyCoV-D the world's first plasmid DNA vaccine for Covid-19. ZyCoV-D is a three-dose vaccine which will be administered first on day zero, day 28th and then on the 56th day. With this approval, India now has its first Covid-19 vaccine for the adolescents in the 12-18 age group…," the company said.

It said the vaccine is delivered via a "painless" intradermal applicator and added that it plans to seek approval for a two-dose regimen of the vaccine. "The main advantage of DNA vaccines is their ability to stimulate both the humoral and cellular arms of the adaptive immune system. They are a valuable form of antigen-specific immunotherapy, as they are safe, stable and can be easily produced," the company said.

An official, who asked not to be named, said the expert panel sought more data to allow the company's existing request to approve it as a two-dose shot.

A second government official, who asked not to be named, said final approval to roll-out the vaccine to children above the age of 12 will be taken by government's expert committees on vaccination. "The emergency use approval has come for the Zydus vaccine for use in 12 year olds and above but it will be the call of the experts on panels such as NTAGI (National Technical Advisory Group on Immunisation) and NEGVAC (National Expert Group on Vaccine Administration for Covid-19), who decide on Covid-19 vaccine-related matters, whether to allow Covid-19 vaccination in children; and when. Even if the experts allow it, orders will have to be placed -- there is an entire procurement process that needs to be followed. Regulatory approval is just a part of the process," this person said.

ZyCoV-D was developed in partnership with the government's Department of Biotechnology under the 'Mission Covid Suraksha', which involved the pooling of resources by several Indian research institutions for development and clinical trials.

The vaccine works by instructing cells to produce the spike protein of the Sars-CoV-2 virus, which elicits an immune response, the ministry of science and technology said in a statement on Friday.

"It is a matter of great pride that today we have the EUA for the world's first DNA Covid-19 vaccine ZyCoV-D by Zydus developed in partnership with the Department of Biotechnology and supported through Mission Covid Suraksha. The Indian Vaccine Mission Covid Suraksha was launched under the Atma Nirbhar Bharat package 3.0 being implemented by BIRAC, is aimed at the development of safe and efficacious Covid-19 vaccines for public health," said Dr Renu Swarup, secretary, department of biotechnology, and chairperson, Biotechnology Industry Research Assistance Council.

"We are confident that this will be an important vaccine for both India and the world. This is an important milestone in our indigenous vaccine development mission and positions India on the global map for novel vaccine development," she added.

There are two vaccine candidates that have been tested among children in India: Bharat Biotech's Covaxin and Zydus Cadila's ZyCoV-D. The two are also the only ones of the six now approved in India to be developed indigenously.