The world's first DNA-based COVID-19 vaccine, ZyCoV-D won emergency authorisation from Indian regulators last month. From October, the company, better known as Zydus Cadila, will produce 10 million doses a month.
The health ministry did not immediately respond to a request for comment. The sources sought anonymity because they were not authorised to talk to media.
The vaccine is the only one approved for children in India, which has given a total of 825.9 million doses to adults among its population of nearly 1.4 billion.