More and more U.S. counties with low vaccination rates are starting see Covid cases climb, putting residents at risk for “unnecessary” infections, hospitalizations and potentially deaths as the delta variant tears through the country, according to U.S. health officials.

“After several weeks of declining numbers of cases, followed by a long plateau, we are seeing an increase in the number of cases in many parts of the country now,” Dr. Jay Butler, deputy director for infectious diseases at the CDC, said on a call hosted by an industry group Tuesday. Hospitalization rates, which tend to lag confirmed cases, are similarly starting to climb, he said.