Prime Minister Narendra Modi said today that the world's biggest inoculation drive against coronavirus is set to begin in the country, a day after the drugs regulator approved two vaccines for restricted emergency use. India's drugs regulator on Sunday approved Oxford COVID-19 vaccine Covishield, manufactured by the Serum Institute, and indigenously developed Covaxin of Bharat Biotech for restricted emergency use in the country, paving the way for a massive inoculation drive.