In a first, the UK has launched a new clinical trial that will assess the efficacy of a third 'booster' dose of seven different Covid-19 vaccines on patients' immune responses.<br />'' <br />''The trial will assess Covid-19 vaccines of Oxford-AstraZeneca, Pfizer-BioNTech, Moderna, Novavax, Valneva, Janssen and Curevac.<br />'' <br />''The trial, named Cov-Boost, aims to begin in June and recruit 3,000 people of all ages who had their first dose in December or January, to test if this is worthwhile.<br />'' <br />''It costs 19.3 million pound and is being funded by the UK government and led by the University Hospital Southampton NHS Foundation Trust.<br />'' <br />''The trial will be conducted at 18 sites across the UK, and half doses will also be tested.<br />'' <br />''Besides data on side-effects and immune responses, the findings will also help vaccine advisers decide if re-vaccinating some people in the autumn is necessary.<br />'' <br />''<span style="color: #222222;">The participants will be asked to keep diaries of any side-effects after a third dose, and their immune responses will be tested after one, three and 12 months.</span><br />