Covaxin was developed by Bharat Biotech in collaboration with ICMR and NIV, Pune.
Covaxin, India's first indigenous vaccine against COVID-19, showed enhanced immune response without any serious side effects in the Phase 1 trials, according to the results published in well-respected Lancet Infectious Disease journal on Friday.
Similar peer-reviewed studies for the Phase 2 are still awaited and Phase 3 trials are ongoing even as the government continues to give out the jabs to lakhs of front-line workers. While the first two phases of vaccine trials usually focus on their safety, the third stage generally determines its efficacy.
Developed by Bharat Biotech in collaboration with the Indian Council of Medical Research (ICMR) and the National Institute of Virology (NIV), Pune, Covaxin has been granted emergency use authorisation in clinical trial mode by the Indian government.
The vaccine, which uses an inactivated virus to trigger an immune response, had raised concerns among experts over its emergency approval earlier this month by India's drug regulator while the Phase 3 trials are still underway.
The vaccine, codenamed BBV152, was well tolerated in all dose groups with no vaccine-related serious adverse events, noted the authors of the Lancet study funded by Bharat Biotech.
The same results were earlier published in the preprint server medRxiv in December.
However, there has been no new data released in the public domain which could demonstrate further its safety and efficacy.
The authors said that all adverse events were mild and moderate, and were more frequent after the first dose, adding that one adverse event was reported but was unrelated to the vaccine.
The randomised Phase 1 trial was carried at 11 hospitals across India. Adults aged 18-55 years who were deemed healthy by the investigator were eligible. Two intramuscular doses of vaccines were administered 14 days apart.
The most common adverse event was pain at the injection site, followed by headache, fatigue, and fever.
India began one of the world's biggest vaccination programmes on Saturday, using the two locally-made shots Covaxin and Covishield, licensed from Oxford University and pharmaceutical giant AstraZeneca.
The vaccination drive will inoculate 3 crore healthcare and other front-line workers first in the queue, followed by about 27 crore people older than 50 or deemed at high-risk because of pre-existing medical conditions.
Known as the pharmaceutical capital of the world, the country has gifted vaccines to neighbours and partners such as Bangladesh, Nepal, Bhutan, Seychelles, Mauritius and the Maldives. It is starting commercial shipments to Brazil and Morocco on Friday.
(With inputs from agencies)