The federal government is pouring billions of dollars into the effort to develop a vaccine against the coronavirus. At least four pharmaceutical companies say they are ready to conduct vaccine trials on human volunteers—a needed step before widespread distribution. Scientists emphasize the importance of testing the vaccine in diverse populations. Leaders of at least three tribes, the Navajo Nation, the Lummi Nation and the Nooksack Indian Tribe, agreed to allow vaccine trials involving their citizens. But many of those citizens harbor distrust of scientific experiments because of previous missteps.