France, March 5 -- India's first locally-developed Covid-19 vaccine posted 81 percent interim efficacy in late stage trials involving nearly 26,000 people, putting to rest doubts and debate over the shots and brightening prospects of its export to Brazil, and other countries.

Bharat Biotech, the manufacturer, hailed the verdict as "an important milestone in vaccine discovery, for science and our fight against coronavirus" and said the exercise involved the largest cluster of volunteers in a clinical trial in India.

The vaccine jointly developed by Biotech and state-run Indian Council of Medical Research was authorized for emergency use in January even while the trials were underway.

The report also drew praise from public health expert...