A pivotal trial of vaccines against the strain of Ebola that is driving a deadly outbreak across parts of Africa has begun in the Democratic Republic of Congo, where the epidemic originated and the vast majority of cases and deaths have occurred. The first participant was vaccinated on Friday in Bunia, eastern Congo, with Merck & Co.’s Ervebo shot, which has been approved to guard against a different Ebola species. An experimental alternative developed specifically against Bundibugyo by Moderna Inc. and another by the University of Oxford and Serum Institute of India could also be tested in the study within weeks.“I’m pretty confident that we have the window because the outbreak is not being brought under control,” Coalition for Epidemic Preparedness Innovations Chief Executive Officer Richard Hatchett said in an interview. Congo recorded 9,704 confirmed cases and 4,687 deaths as of October 20, according to the World Health Organization, and is the largest Ebola outbreak ever recorded in the country, irrespective of virus species. Infections linked to the outbreak have also been detected beyond its borders.