COVID-19 vaccine and evaluate potential incremental benefits for the duration of protection with a second dose.The U.S. drugmaker plans to enrol up to 30,000 participants for the study and run it in parallel with a one-dose trial with as many as 60,000 volunteers that began in September.The UK arm of the study is aiming to recruit 6,000 participants and the rest will join from other countries with a high incidence of COVID-19 cases such as the United States, Belgium, Colombia, France, Germany, the Philippines, South Africa and Spain, it said.They will be given a first dose of either a placebo or the experimental shot, currently called Ad26COV2, followed by a second dose or placebo 57 days later, said Saul Faust, a professor of paediatric.