UK Announces World’s First Trial of Switching COVID-19 Vaccines Between Doses

A vial of the COVID-19 vaccine developed by Oxford University and UK-based drugmaker AstraZeneca is checked as they arrive at the Princess Royal Hospital in Haywards Heath, England, on Jan. 2, 2021. Gareth Fuller/Pool via AP

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.