LONDON – The U.K. government has accepted the recommendation of medical experts and will begin the rollout of COVID-19 boosters from next week, using mRNA vaccines only. That follows data from the U.K. Cov-Boost trial, looking at combinations of initial and booster doses. The results showed Pfizer Inc./Biontech SE’s and Moderna Inc.’s products generated the best immune responses, regardless of which vaccine was administered initially.