With the Drug Controller General of India (DCGI) approving Serum Institute of India's 'Covishield' vaccine and Bharat Biotech's 'Covaxin' for emergency use, paving way for their roll-out and administration to millions, Russian Sputnik V vaccine makers have said that they are working with AstraZeneca (AZ) to take the efficacy of AZ vaccine to over 90 per cent.