Johnson & Johnson has halted clinical trials of its potential COVID-19 vaccine due to an unexplained illness in a study participant, delaying one of the strongest efforts to contain the global pandemic. The decision comes around a month after AstraZeneca also suspended trials of its experimental coronavirus vaccine — which uses a similar technology — due to a participant falling ill. J&J said that the illness was being re looked by an independent data and safety monitoring board as well as the U.S. group’s clinical and safety physicians.