booster jabs for all Americans from 20 September starting eight months after a person has been fully vaccinated. The development comes as scientists and health experts grapple with how to beat back the surging Delta variant of Covid-19, and follows an extensive debate over whether a third injection of the Pfizer-BioNTech and Moderna vaccines would be appropriate. "The available data make very clear that protection against (coronavirus) infection begins to decrease over time following the initial doses of vaccination, the nation's top health officials, including Centers for Disease Control and Prevention director Rochelle Walensky and US Surgeon General Vivek Murthy, said in a statement. "In association with the dominance of the Delta