People in rural areas are receiving the Covid-19 vaccines at a lower rate than those in urban areas, potentially hindering the nation’s progress toward ending the pandemic, according to a new study published Tuesday by the Centers for Disease Control and Prevention.

The CDC analyzed county-level vaccine administration data among American adults who received their first dose of either the Pfizer–BioNTech or Moderna Covid-19 vaccine or a single dose of the Johnson & Johnson Covid-19 vaccine. It looked at data from 49 states and the District of Columbia through April 10.

The agency found a lower percentage of residents in rural counties who received at least one shot than in urban counties, at 38.9% and 45.7%, respectively. The CDC also found people in rural areas who did receive a vaccine often had to travel farther to get it than people in urban areas.

“Vaccine hesitancy in rural areas is a major barrier that public health practitioners, health care providers, and local partners need to address to achieve vaccination equity,” the CDC wrote in the report.

“As availability of COVID-19 vaccines expands, public health practitioners should continue collaborating with health care providers, pharmacies, employers, faith leaders, and other community partners to identify and address barriers to COVID-19 vaccination in rural areas,” the agency added.

The new data comes as more studies find rural residents may be more hesitant to get a vaccine. A Kaiser Family Foundation report published in April found 3-in-10 rural residents said they will either “definitely not” get vaccinated or will do so only if required.

CDC Director Dr. Rochelle Walensky addressed the study before it was released Tuesday, saying the Biden administration was committed to reaching out to communities “in every corner of the United States.”

The U.S. is working to “make sure vaccine access is equitable regardless of whether you live in rural or urban areas,” she said during a White House Covid-19 briefing. “Public health staff are working nationwide to provide trusted information via trusted messengers.”

Walensky said over the past weekend CDC staff attended the Talladega Superspeedway in Alabama where U.S. health officials provided Covid testing and vaccinations.

“We are truly making strides across the country to ensure people have access to vaccines,” she said.

The study Tuesday did not calculate coverage by race and ethnicity, the CDC said, because information on that was missing for 40% of the data.