On Monday, the opening day of the world's largest AIDS conference, U.N. Secretary-General Ban Ki-moon struck a somber tone, saying that the gains that have been made in the global fight against the virus are "inadequate — and fragile."

Ban's remarks are striking given the optimism that has prevailed about the disease in recent years thanks to new drugs that have helped those infected have life expectancies similar to those of people who are not infected and stopped many others from getting infected in the first place. Many world leaders — including Hillary Clinton, the presumed Democratic presidential nominee, and National Institutes of Health Director Francis Collins — have even dared to use the word "cure" when talking about HIV/AIDS.

Speaking to reporters in Durban, South Africa, at the 21st International AIDS Conference, Ban pointed out that the progress being made is unequal. More than half of the 36.9 million people estimated to be living with HIV worldwide still lack access to treatment. In developed countries, lack of access to medications often has to do with stigma and discrimination and while that barrier is a major issue in poorer countries, too, the burden of the high prices of drugs can be greater. About 1.2 million are expected to die each year from HIV and related complications.

"Many people cannot afford the new generation of treatments for AIDS," he said.

Ban also took the scientific community to task for the lack of research on neglected and rare diseases. Tuberculosis, he noted, is the leading cause of death for people living with HIV, but there haven't been any new medications to treat it in years.

In essence, Ban's words were a plea against complacency, and he emphasized how important it is to look at AIDS in the context of other global health threats.

"The bigger health picture is worrying. We are reactively addressing threats like Ebola and Zika. Antimicrobial resistance is a major threat that could kill as many as 10 million people a year by 2050 — if we fail to act," he said.

Ban said that he has convened a panel on access to medicines and that it will issue a report with policy recommendations for how to break down some of these barriers to treatment.

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