New Trial Tests Mixing br 2 Different COVID-19 Vaccines .br The clinical trial launched in br the United Kingdom on Thursday.br As part of the study, patients will receive one br dose of the AstraZeneca vaccine, followed by br a dose of the Pfizer vaccine or vice versa.br The U.K.’s Department of Health said the trial is the br first of its kind and will test the safety of mixing br vaccines for first and second doses.br The study, named “Com-Cov,” will br span over 13 months and provide br its initial findings by summer.br This is a hugely important clinical trial that will provide us with more vital evidence on the safety of these vaccines when used in different ways, Minister for Covid-19 vaccine deployment br Nadhim Zahawi, via statement.br The Centers for Disease Control and Prevention in the U.S. recently changed its guidance to say the Moderna and Pfizer vaccines could be mixed in "exceptional situations.