UK Study Will Test If Getting Doses Of 2 Different COVID-19 Vaccines Is Effective A new vaccine trial is underway in the U.K. to test whether mixing and matching different COVID-19 vaccines for the first and second doses is effective, BBC News reports. The country is currently using the Pfizer-BioNTech vaccine and Oxford-AstraZeneca vaccine, which both require two doses. For the study, run by the National Immunisation Schedule Evaluation Consortium, patients will get one dose of each. The trial will involve 800 volunteers, age 50 or older, who haven't received a COVID-19 vaccine yet. They will receive their two vaccine doses as usual, four or 12 weeks apart, but one will be the Oxford shot and the other will be the Pfizer shot. If regulators approve other vaccines for use, they may be added to the study.