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 west to Texas and north to southern Missouri. The clusters also include parts of Alabama, Arkansas, Louisiana, Oklahoma and Tennessee, and are made up of mostly smaller counties but also cities such as Montgomery, Alabama; Shreveport, Louisiana; and Amarillo, Texas.
Most of these states are currently seeing increases in Covid-19 cases.
Those vulnerable clusters put all of the United States — and to some extent, the world — at risk for going back to 2020, since high-transmission areas can become breeding grounds for Covid-19 variants that could go on to evade Covid-19 vaccines.
“These clusters of unvaccinated people are what is standing in the way of us putting this virus down permanently,” said Dr. Jonathan Reiner, a CNN medical analyst and professor of medicine and surgery at George Washington University.
Millions of unvaccinated people in the clusters
The county data is not without its flaws. When someone gets a shot, their home county is supposed to be noted in state records, but the system doesn’t always work perfectly. In the Georgetown analysis, at least 90% of all vaccinations were recorded with the person’s home county, Bansal said.
In some cases, the Georgetown data differs from CDC data because Bansal and her team were able to obtain additional data directly from state health departments.
While the clusters do encompass some sizable cities, 92% of the counties in the clusters have a population of less than 100,000.
The federal government has been engaging with churches and organizations such as the YMCA to encourage Covid-19 vaccination in areas like these, US Surgeon General Dr. Vivek Murthy told CNN.
“These are extraordinary partners in reaching communities [in rural areas] where health care access isn’t as easy as it is in urban areas,” he said.
Clusters give virus opportunities to mutate
The Delta variant, which now comprises more than half the cases in the United States, is the latest in a long string of Covid-19 variants that have spread more easily and in some cases caused more severe illness.
That’s why the clusters are so worrisome. Each time a virus spreads, it has an opportunity to learn how to mutate.
“We know that if you give the virus the opportunity to circulate and replicate, you give it the opportunity to generate more variants,” Dr. Anthony Fauci, President Joe Biden’s chief medical adviser, told CNN.
The Delta variant has learned how to evade Covid-19 vaccines to a small degree, but they still offer excellent protection against severe disease and hospitalization.
The fear is that the next variant might be able to outsmart the vaccine more thoroughly, causing problems even for parts of the country that have high vaccination rates.
“We’ve been lucky with the variants so far that they’ve been relatively susceptible to our vaccine, but the more you roll the dice, the more opportunities there will be for a resistant variant,” Reiner said.
CNN’s Justin Lape contributed to this report.