Volunteer Danica Marcos, sits in a park in London, Friday, Oct. 16, 202. UK researchers are preparing to begin a controversial experiment that will infect healthy volunteers with the new coronavirus to study the disease in hopes of speeding up development of a vaccine. (AP Photo/Frank Augstein)
In the United States, the National Institutes of Health has downplayed the need for challenge studies given the speed with which vaccines are being developed, but it has taken preliminary steps to prepare for such research in case the approach eventually is required. Those steps include examining the ethics of a challenge study, and funding research to create lab-grown virus strains that potentially could be used.