Mixing vaccine doses triggers more pronounced short-term side effects in people when compared to administering two shots of the same Covid jab, new research has shown. First launched in February by researchers at Oxford University, the Com-Cov study is examining whether doses of the Oxford/AstraZeneca and Pfizer/BioNTech vaccines can be safely mixed. The treatment, known as a heterologous prime-boost, can only be administered with licensed jabs...