Amid a rise in Covid cases in several countries, official sources on Wednesday said that the Serum Institute of India (SII) has offered 20 million coronavirus vaccines, Covishield, free of cost to the central government. The source said that the Director of Government and Regulatory Affairs at the Serum Institute, Prakash Kumar Singh, has in written offered the vaccine doses worth Rs 420 Crore ($50 million) free of cost to the Indian government, PTI reported.