The rapid expansion of COVID-19 vaccinations to senior citizens across the U.S. has led to bottlenecks, system crashes and hard feelings in many states because of overwhelming demand for the shots. Mississippi’s Health Department stopped taking new appointments the same day it began accepting them because of a “monumental surge” in requests. … In California, counties begged for more coronavirus vaccine to reach millions of their senior citizens. Hospitals in South Carolina ran out appointment slots within hours. Phone lines were jammed in Georgia.