A veteran public health expert warned top Indian officials in early March this year that a new variant of the coronavirus was spreading quickly in a rural district in the heart of the country and that the outbreak required urgent attention, Reuters reports.

Federal health authorities failed to respond adequately to that warning, Dr Subhash Salunke, who has 30 years of experience in public health in India, Indonesia and the United States, told the news agency.

The variant, now known as B.1.617, triggered a catastrophic wave of coronavirus cases in India and has since spread to more than 40 other countries. In May, the World Health Organisation termed it a "variant of concern," citing its high transmissibility.