The Centers for Disease Control and Prevention on Wednesday proposed guidelines for distributing a coronavirus vaccine in the United States if and when one is approved for public use.

The guidelines, unveiled during a presentation at the CDC’s Advisory Committee on Immunization Practices meeting, would prioritize health-care workers, essential personnel and vulnerable Americans, like the elderly and those with underlying health conditions. 

It would include all paid and unpaid people working in health-care settings. That includes hospitals, long-term care facilities, home-based care, outpatient centers and pharmacies. The CDC estimates there are between 17 million and 20 million health-care workers in the U.S.

Essential personnel, which the CDC estimates make up 60 million to 80 million of the population, working in food and agriculture, transportation, education, energy, wastewater and law enforcement would also be among the first to get the vaccine, according to the proposal.

About 100 million people with medical conditions and 53 million people over the age of 65 would get a vaccine. 

There are currently no approved vaccines for the virus, which has infected 5.7 million Americans and killed at least 178,500, according to data compiled by Johns Hopkins University. 

As public health officials and pharmaceutical companies race to find a safe and effective vaccine by the end of the year, scientists and infectious disease experts worry about who will get the vaccine first and how. The U.S. will initially have a limited supply of vaccine doses that won’t be widely available until “several months” into 2021, according to Dr. Anthony Fauci, the nation’s leading infectious disease expert.

Many experts have said the vaccine should go to the most at-risk groups first, including health-care workers, the elderly as well as poor and minority communities, which have been disproportionately impacted by the virus. 

Earlier this month, President Donald Trump told reporters at a White House press briefing that a coronavirus vaccine should probably go to the elderly or those most vulnerable people first, though he added he would rely on a doctor’s expertise for that decision. ”We’re actually making a list right now. Mostly nursing homes, retirement centers,” he said on Aug. 14. 

The CDC also noted in its guidelines Wednesday that it will be difficult to conduct vaccinations while also practicing social distancing. 

The agency said health-care settings like provider offices or pharmacies could be better suited to provide vaccination. It may be difficult for health-care workers to reach rural areas, minorities and populations with limited access to health care, the CDC said. 

The CDC also said it is preparing for the possibility of distributing different kinds of vaccines at once.

The U.S., as part of the Trump administration’s Operation Warp Speed initiative, has already invested millions of dollars in six potential vaccines, including from drug companies Pfizer and Moderna, which entered phase three trials last months. There’s a chance the vaccine could be ready around the same time. 

Trump has previously said the U.S. would use the military to distribute the vaccine, but officials from the White House and the U.S. Defense Department have disputed that.