India's Bharat Biotech said on Wednesday a booster shot of its Covaxin Covid-19 vaccine administered six months after the last of two doses neutralises both the Omicron and Delta variants of the coronavirus.

The study was conducted at the Emory Vaccine Center in Atlanta based on blood serum collected from 13 individuals, 28 days after their booster shot. It was sponsored by Bharat Biotech's partner Ocugen Inc.

“The neutralisation activity of Covaxin-boosted sera was comparable to what has been observed in mRNA vaccine-boosted sera against the Omicron variant,” Bharat Biotech said in a statement. “More than 90% of all individuals boosted with Covaxin showed neutralising antibodies.”

Covaxin, India's first domestically developed Covid-19 vaccine, received a WHO emergency-use listing late last year. More than 201 million doses of it have been administered in the country.