Alex Azar served as secretary of U.S. Health and Human Services from 2018 to 2021, spearheading the department’s COVID-19 response and overseeing Operation Warp Speed, the public-private partnership to expedite COVID-19 vaccines. Donna Shalala, the longest-serving HHS secretary (1993 to 2001), worked to create, implement and oversee the Children’s Health Insurance Program and helped raise childhood immunization rates to record levels, among other accomplishments.