British investigators will evaluate in a trial the efficacy of mixing COVID-19 vaccine doses from Pfizer and AstraZeneca to possibly decrease the number of coronavirus infections as new variants are being discovered. "All manufacturers, Pfizer-BioNTech, Moderna, Oxford-AstraZeneca and others, are looking at how they can improve their vaccine to make sure that we are ready for any variant -- there are about 4,000 variants around the world of COVID-19 now," said British Vaccine Deployment Minister Nadhim Zahawi.