The number of medical schools that offer MD/PhD programs with PhDs in social sciences is limited.
Most MD/PhD programs are designed for PhDs in biomedical sciences.
Here’s AMCAS’s list of MD/PhD programs:
https://www.aamc.org/students/download/62760/data/faqtable.pdf
Column 8 lists what fields other than biomedical sciences are offered by individual programs.
29 programs offer PhDs in Public health; only UPenn offers a PhD in health care economics.
The American Physician Scientist Association has its own list of purely social science/humanities (SSH) MD/PhD programs here:
http://www.physicianscientists.org/?page=SSH
Again the number of schools offering these programs is quite limited.
ETA: Here’s AMCAS’s webpage for–
MD-PhD in the Social Sciences or Humanities: Is it Right for Me?
https://www.aamc.org/students/research/mdphd/420992/md-phdsocialscienceshumanities.html