In April, Hegseth said the flu shot would be optional for military personnel. ByDr. Jade Cobern, Luis Martinez, Mary Kekatos, and Steven Beynon Front view of the Chapman Training Annex entry gate in San Antonio, Texas, Aug. 17, 2024. The Chapman Training Annex is a part of Joint Base San Antonio. Carlos Kosienski/Sipa USA via Reuters A flu outbreak at the Air Force's basic training hub in San Antonio is worsening, according to two sources familiar with the situation.