Indian drugmaker Bharat Biotech’s coronavirus vaccine, which has been authorized for use in the country, proved safe and produced an immune response in a small group of adults aged 18 to 55, according to a study published in The Lancet medical journal.

The vaccine, developed with the Indian Council of Medical Research (ICMR), is being evaluated in a separate 25,800 person trial, which started in November. Bharat Biotech said on Friday 13,000 people participating in the late-stage trial had been given the second dose.

The interim data published here in the journal included three different vaccine formulations and a placebo group among 375 adults.

Two formulations of the vaccine, called COVAXIN, have been selected for more advanced stages of testing and further efficacy trials are warranted, the report said.

COVAXIN is an inactivated vaccine that introduces dead virus into the body to trigger an immune response.

This is the first peer reviewed data for the vaccine that has come under scrutiny after widespread criticism over the lack of transparency on the approval process for the shot.

The vaccine was granted emergency approval by the drugs controller general of India this month along with another vaccine, Covishield, developed by AstraZeneca and Oxford University.

India, which has reported the highest number of coronavirus infections after the United States, kicked off its own vaccination drive on Saturday in what the government called the “world’s largest vaccination program.”