Moncef Slaoui, chief advisor to Operation Warp Speed, the public-private partnership to hurry along a vaccine for COVID-19, cited tough going in the early days of development, as researchers met “a real challenge to engage the population.” During a panel discussion at the virtual 39th J.P. Morgan Healthcare Conference, he pointed to “a double-edged sword, to talk about what a vaccine can do, when we don’t know – and then once you know, you’re going to have to change your message.”