Why officials are particularly concerned about unvaccinated population in the South

State health departments report that the "vast majority" of hospitalized COVID-19 patients are unvaccinated

Although national coronavirus metrics have been declining rapidly, infections in areas with low vaccination rates persist -- a particularly worrisome trend, experts say, as new, and more transmissible variants emerge. Health experts have been emphatic in their message that the best way to curtail the spread of the highly infectious, and potentially more dangerous, delta variant, which the Centers for Disease Control and Prevention now classifies as a "variant of concern," is to get fully vaccinated. "People who are unvaccinated will be at heightened risk in the coming months," Caitlin M. Rivers, an epidemiologist and senior scholar at The Johns Hopkins Hospital, told ABC News. A recent ABC News analysis of county-level data from the CDC and the Department of Health and Human Services found that per capita, hospitalization rates are twice as high in counties with the lowest rates of fully vaccinated residents, than in counties with the highest rates of fully vaccinated residents.