More than half of American HIV patients aren’t getting treatment, according to the Centers for Disease Control and Prevention. And a lack of affordable medicine plays a big part.

According to CDC data published Monday, some 1.2 million people in the United States are living with HIV. Of this group, 30 percent are “virally suppressed,” which means they are getting medication to reduce the function and replication of the virus. But 86 percent of the remaining patients were not undergoing any kind of medical treatment.

Mitchell Warren, executive director of HIV prevention nonprofit AVAC, told Bloomberg that, along with the social stigma, the coverage gaps in the American health care system are a major reason why people aren’t receiving treatment -- which doesn’t come cheap.

HIV, which can lead to AIDS,  requires lifelong medical treatment, which can cost hundreds of thousands of dollars per patient. According to Healthline, a medical information site, a 15-day supply of a common HIV drug called Etravirine costs roughly $510,  another drug, Efavirenz, costs about $863 for a 90-day supply. And with no generic versions available, the costs can add up fast.

In some cases, patients who can’t afford to pay are eligible for Medicaid or Medicare. The CDC data, which is from 2011, doesn’t show the impact of the Affordable Care Act, but there are still 21 states that aren’t expanding these programs.

“In states that do not expand Medicaid, many adults will fall into a coverage gap of having incomes above Medicaid eligibility limits but below the lower limit for marketplace premium tax credits,” says a report from the Kaiser Family Foundation, which also outlines how most of the uncovered people are likely to be racial or ethnic minorities, who are also much more likely to contract HIV.

The majority of HIV funding in the United States comes from the federally mandated Ryan White Program, which reaches more than 500,000 people who aren’t able to pay for their care. In 2013, the program disbursed $631 million in “emergency relief” and more than $1 billion for HIV care.

Recently, insurance companies Cigna and Coventry Health Care said they would put a $200 monthly cap on the amount Florida patients pay for common HIV drugs such as Atripla, Complera, Stribild and Fuzeon on the federal health care exchange. The move was a response to complaints from advocacy groups such as the AIDS Institute and the National Health Law Program.

However, the policy only applies to patients in Florida. Advocacy groups such as the ONE Campaign are hailing the recent changes, but note that authorities still have a long way to go.

“On the whole it is clear that increased overall resources to fight the disease, applied and targeted more effectively, have helped to accelerate progress at the global level,” reads the organization's latest report. “But equally clear is the fragility of this progress.”