BananaStock via Getty Images

There is still no cure or vaccine for HIV/AIDS, which affects approximately 37 million people around the world. But there is reason to hope that the global response to this pandemic is improving.

Fewer people died of HIV in 2015 than at any point in almost 20 years, while new HIV infections are at the lowest point since 1991, the World Health Organization noted in its 2016 progress report. That may be, in part, because at least two million new people began taking antiretroviral therapy in 2015, the largest annual increase ever in the history of the disease.

For World AIDS Day, we asked researchers and experts to weigh in on any other significant scientific discoveries and treatment strides worth celebrating this year. Read on to learn about the strides in vaccine development, functional cures and historical understanding that 2016 brought.

1. Geneticists exonerated “Patient Zero.”

Perhaps no single person has borne more blame for the virus’ arrival in the U.S. than Gaétan Dugas, better known as “Patient Zero.” Dugas was a French Canadian flight attendant who was presumed to have passed the HIV/AIDS virus to gay communities in the U.S. after contracting the disease during an international trip, according to The New York Times. His supposed role in spreading the epidemic (and the first use of the term “Patient Zero”) was chronicled in the seminal 1987 book And The Band Played On by journalist Randy Shilts.

The only problem? HIV/AIDS was present in the U.S. long before Dugas came to the attention of health officials.

In 2016, a series of intricate genetic tests on blood samples drawn in the 1970s confirmed this, exonerating Dugas. It also turned out that the name “Patient Zero” was itself extremely misleading, and stemmed from a misreading of the pseudonym “Patient O.” The letter “O” stood for “outside California” in a very early study focused on the Los Angeles region that was conducted by the U.S. Centers for Disease Control and Prevention.

Paul Volberding, director of the University of California, San Francisco’s AIDS Research Institute, called the genetic detective study one of his favorite stories in a year full of exciting HIV/AIDS discoveries.

The study was critical in understanding more about HIV/AIDS, said Jennifer Brier, director and associate professor of Gender and Women’s Studies at the University of Illinois at Chicago. But she stressed that, regardless of evidence, it’s problematic and counterproductive to assign blame to one person or one region for the virus’s spread.

“It perpetuates the idea that HIV/AIDS had to come from somewhere,” Brier wrote in an email to HuffPost. “I am not sure that this model of shifting the blame... solves the larger problem of addressing how we now deal with HIV/AIDS as a global pandemic.”

2. The NIH made a discovery that may lead to an HIV vaccine.

The HIV virus is impossible for the human immune system to defeat on its own because the pathogen can quickly mutate to change its surface proteins, evading detection. But a newly discovered antibody ― a protein produced by the body’s immune system to destroy invading pathogens ― can powerfully neutralize many variants of the most common strain of HIV.

Prior to this, the most powerful identified antibody could only neutralize about 90 percent of HIV variants. This latest discovery, the N6, can neutralize 98 percent. Scientists at the National Institutes of Health isolated the N6 antibody from the blood of a person with HIV.

N6 is so adept at neutralizing HIV because it can identify and attach to the parts of the virus that remain relatively consistent from mutation to mutation. It also appears to avoid the sugars on the surface of the virus that tend to block antibodies from attaching.

“We have an antibody now that essentially compensates for most of the diversity of the virus,” said Dr. Justin Bailey, assistant professor of medicine at Johns Hopkins University School of Medicine, in a previous HuffPost report. “The next big step is trying to design a vaccine that could induce an antibody like this, because if you could induce an N6-like antibody at high enough levels in vaccinated people, they’d probably all be protected against most HIV infections.”

However, experts caution it could take more than 10 years before anything like a vaccine can be tested and created.

3. A two-part treatment successful in monkeys is giving scientists hope for a cure.

An experimental HIV vaccine combined with a compound that can stimulate the immune system managed to suppress SIV (a simian version of HIV) to undetectable levels in monkeys, as if they were taking antiretroviral therapy, or ART.

The exciting finding was limited to three out of the nine monkeys who received the experimental combination, but the result showed promise that scientists may one day be able to create a “functional cure” for HIV. In other words, people may one day be able to suppress their viral levels without the need for costly, daily ART treatments.

“If all the animals went undetectable in the absence of [ART treatments], that would have been a home run,” lead study investigator Daniel Barouch previously told HuffPost. “I would say that what we achieved was a solid base hit, and it’s something that we can work from.”

Volberding, who wasn’t involved in the study, called the study results “a real first,” and said it was an encouraging sign in cure research.

Barouch now hopes to test the combination approach in humans.

4. A drug that’s already on the market for unrelated diseases works as an HIV suppressant.

In another monkey trial, scientists from the NIH and Emory University were able to suppress SIV to undetectable levels by supplementing antiretroviral therapy with an antibody that is similar to vedolizumab, a treatment already approved in the U.S. for other diseases. Generally, HIV levels rebound within weeks of stopping medication, but among all eight of the monkeys who received the experimental treatment, virus levels remained undetectable for almost two years.

The best part? “The antibody is literally on pharmacy shelves, as it’s approved as a treatment for ulcerative colitis and Crohn’s disease,” said Volberding, who wasn’t involved in the study.

Vedolizumab works by preventing the body’s immune cells from entering the intestines, a body part that typically sustains a lot of damage during the initial stages of HIV infection. The thought is that preventing these immune cells from entering intestinal tissues protects them somehow. However, it still isn’t clear why saving those immune cells from destruction helped the animals suppress their SIV levels, said senior study author Aftab Ansari, a professor of pathology and laboratory medicine at Emory School of Medicine and Yerkes National Primate Research Center.

Based on the results in monkeys, the NIH has begun trials to test vedolizumab’s ability to suppress HIV levels in people. It’s important to note that the monkeys were infected with SIV for just five weeks before scientists put them on a course of ART and eventual antibody treatment, which means it’s possible that the length of infection may affect the efficacy of this treatment. A 2015 study among 15,000 men in the Netherlands found that those who developed HIV some time between 1980 and 2011 took an average of about three years to learn of their infection toward the latter end of the study time period.