Made by Bharat Biotech, iNCOVACC is administered in the form of drops and stimulates an immune response in the tissues that line the nasal cavity.

In September 2022, China had approved an inhaled Covid vaccine, administered in the form or a spray.

Scientists say that nasal vaccines may offer added immunity in the lining of the nose and upper airways, where Covid typically enters the body.

Research teams in the UK and the US have also been investigating nasal spray vaccines.

In November, India's drug regulator approved the use of iNCOVACC as a heterologous booster dose - a booster for people who had previously received two doses of Covishied or Covaxin, the two main Indian vaccines - in emergency situations among adults.

In December, it was approved by the drug regulator as a primary vaccine and as a subsequent booster shot in adults.

The vaccine will cost 800 rupees ($10; £8) per dose in private hospitals and 325 rupees per dose in government hospitals and can be booked on the government's online platform. Two doses are to be taken 28 days apart.

iNCOVACC uses a adenovirus as a carrier for the genetic code that teaches the body how to fight the infection. Adenoviruses used in the vaccines are harmless transporters which have been modified so they cannot replicate or cause infection.

Dr Krishna Ella, chairman of Bharat Biotech, told ANI news agency that the vaccine was "easy to deliver" as it didn't need a syringe or needle, and that it produced a broader immune response as compared to injectable Covid vaccines.

India has administered over two billion Covid jabs so far. More than 70% of the Indian population has taken at least two doses, according to the federal health ministry.

In January 2022, India began giving boosters to healthcare and frontline workers, and those above 60 years with comorbidities. It was later expanded to all adults. However, the pace of booster doses administrated has been slow.