How one disease 'frightened us to the core, brought death to our door' - and then 'changed everything'
Officials then estimated that the number of people with HIV, the virus that can lead to AIDS, was somewhere between five and 10 million.
At the time, misinformation about what a diagnosis meant and how the disease spread was rampant.
"There was a stigma of fear," James Bunn, who founded World AIDS Day, explained to NPR in 2011. "There was a lot that people felt they did not know about the epidemic and they were afraid. And they were right to be afraid because of the things that they were hearing."
Unlike many other viruses, the body cannot get rid of HIV over time, so those that contract the virus have it for life.
Before the advent of effective treatments, AIDS was generally considered a death sentence. HIV would almost inevitably progress into AIDS, which is when the immune system is so weakened by the virus that people start picking up infections and illnesses that a healthy person would easily fight off. After developing AIDS, people lived an average of just ten years without treatment.
Today, about 1.2 million people in the US and 35 million people around the world are living with HIV. Most of them still don't know that they have the virus, which is why increasing access to HIV tests - and encouraging people to get tested - is crucial. But deaths from AIDS have been steadily falling since 2004, when the epidemic peaked.
For years, AIDS activists fought for funding to study and find ways to treat the disease, which was largely ignored in its early years.
Now, thanks to those efforts, increased focus from the United Nations, a surge in government funding, and the work of many scientists and doctors, there are effective medications accessed by a growing share of those infected and much better awareness about the disease and how it spreads.
"The epidemic frightened us to the core, brought death to our door and opened our eyes to the injustice of stigma and discrimination faced by the most vulnerable people among us," Michel Sidibé, the executive director of UNAIDS, wrote earlier this year. "AIDS changed everything."
A whole host of treatments are now available that reduce the amount of HIV in the blood (a measure called viral load) to levels where it is virtually undetectable. With these treatments, HIV does not progress into AIDS and people around the world can expect to live on average about two decades longer than people diagnosed in 2001.
In wealthy countries especially, HIV has become more like a chronic illness than a death sentence. In the US and Canada, a 20-year-old diagnosed with HIV today is expected to live nearly as long as the average adult.
However, it's important to note that many treatments are still very expensive, and only available to those that can afford them. Less than half of people with AIDS are receiving treatment, according to The Economist, though the UN is actively working to bring treatment to more and more people every year.
The majority of people with AIDS live in sub-Saharan Africa, and around the world, AIDS still kills more than a million people every year.
Still, in the US, most HIV patients are getting some form of antiretroviral therapy - a cocktail of pills designed to prevent the virus from making copies of itself. It reduces the viral load, suppresses symptoms, and makes it much harder for a patient to pass the virus to someone else. The UN estimates that antiretroviral therapy saved 7.6 million lives around the world between 1995 and 2013.
But it can be a challenge to get regular access to the pills, and the grueling treatment regimen causes long-term liver damage in some patients.
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There are some alternatives on the horizon. The FDA just approved a once daily pill called Genvoya that has better long-term safety than many other HIV drugs. And drug developers are working on an that patients would only need every four or eight weeks, removing the need the remember to take a pill (or pills) every single day.
Along with the rise of safe sex practices, there are also now pharmaceuticals that can prevent someone from getting the virus in the first place. When used correctly, a pill called Truvada can reduce the risk of HIV infection in people with a high risk of contracting it (those having unprotected sex or taking intravenous drugs) by up to 92%. The problem is that it's only effective if you remember to take it every single day without fail.
Companies are also still trying to create an HIV vaccine that could eliminate the virus once and for all, though some medical professionals are skeptical that it can be done.
While the number of people with HIV is steadily declining, and the effectiveness of treatments is improving, AIDS remains a persistent global health crisis.
And even 27 years after the first World AIDS Day, a diagnosis can still come with a powerful stigma. Charlie Sheen, who recently revealed that he is HIV-positive, said on the "Today" show that he paid people millions of dollars to keep his HIV-positive status a secret.
It's not just celebrities who face a stigma, either. One patient diagnosed in 2007 told NPR: "I was more afraid of the stigma attached to the disease than the actual disease."