The UK government has announced the world’s first clinical trial of switching between different COVID-19 vaccines for the first and second doses. Scientists are hoping that the trial—which won’t yield initial results until the summer—will reveal how vaccines could be used more flexibly, potentially resolving logistical and supply challenges. “It is also even possible that by combining vaccines, the immune response could be enhanced giving even higher antibody levels that last longer; unless this is evaluated in a clinical trial we just won’t know,” said UK Deputy Chief Medical Officer professor Jonathan Van-Tam, who is also overseeing the study. The government emphasised that the current UK vaccine rollout, in which patients take only one vaccine—either Pfizer/BioNTech or Oxford/AstraZeneca—for both doses will not change. Minister for COVID-19 Vaccine Deployment Nadhim Zahawi said, “Nothing will be approved for use more widely than the study, or as part of our vaccine deployment programme, …