CNN — A new data analysis identifies clusters of unvaccinated people, most of them in the southern United States, that are vulnerable to surges in Covid-19 cases and could become breeding grounds for even more deadly Covid-19 variants. The analysis by researchers at Georgetown University identified 30 clusters of counties with low vaccination rates and significant population sizes. The five most significant of those clusters are sprawled across large swaths of the southeastern United States and a smaller portion in the Midwest. The five clusters are largely in parts of eight states, starting in the east in Georgia and stretching...