Two San Antonio military hospitals are taking part in coronavirus vaccine trials, with about 100 personnel participating. Wilford Hall Ambulatory Surgical Center and Brooke Army Medical Center are two of the five Defense Department facilities selected to take part in AstraZeneca's phase-three trial. Researchers in the two-year study hope to enroll a thousand people at higher risk of catching the virus. That would include people over age 65, workers in frontline jobs, and patients with underlying medical conditions.