MARGARET WARNER:Countries around the globe will mark World AIDS Day this weekend. The toll of the disease is still enormous. More than 30 million have died since the epidemic broke out. And AIDS accounted for 1.7 million deaths last year.

But there is growing optimism about curbing and perhaps ending the epidemic for the next generation, even as daunting hurdles remain.

Ray Suarez has the story.

RAY SUAREZ:The numbers are still staggering. Some number 34 million are live well HIV, almost 5 million more than a decade ago. The U.S. substantially increased its commitment to fighting AIDS under President George W. Bush.

Yesterday, Secretary of State Hillary Clinton unveiled the Obama administration's road map to increase access to treatment and eliminate new infections in children by 2015.

SECRETARY OF STATE HILLARY CLINTON: So, as we continue to drive down the number of new infections and drive up the number of people on treatment, eventually, we will be able to treat more people than become infected every year. That will be the tipping point. We will then get ahead of the pandemic and an AIDS-free generation will be in our sight.

RAY SUAREZ:It's been more than 30 years since the first known AIDS cases appeared in 1981. In the early years, contracting AIDS was a near-certain death sentence.

JIM LEHRER: There are few scarier things than the discovery of a new killer disease, one medical science admits is mostly a mystery for which there is no certain cause or cure. Doctors have called the new one bizarre, frustrating, frightening.

RAY SUAREZ:Yet, wider access to drugs in recent years has changed the way people live with AIDS. Deaths have dropped by 26 percent from their highest levels in 2005. New infection rates have fallen by 50 percent in more than two dozen countries, 13 of them in Sub-Saharan Africa.

Those modern achievements are due in part to activists who took on policy-makers and the medical establishment early on to fight for new approaches to treatment.

A new documentary, "How to Survive a Plague," chronicles the uphill journey.

MAN: This is it. This is the plan we're presenting. We need our government to read this plan. We need them to work with us. If they want to change it a little, we will talk to them.

But I want them to adopt it. I want them to get started on it. I want them to save our lives. Thank you.

RAY SUAREZ:These days, governments are doing more. But big problems remain. Some seven million people in developing countries still can't get the drugs they need. And in the U.S., a new report found more than half of HIV-infected young people are unaware of their status.

Dr. Anthony Fauci has been on the front lines of this battle for the past 30 years. He's head of the National Institute of Allergy and Infectious Diseases at the National Institutes of Health, where he joins us this evening.

Dr. Fauci, good to you have with us on the eve another World AIDS Day.

Is there embedded in that statistic, 34 million people living with AIDS, both good news and bad news, that people are living, but still continue to get infected?

DR. ANTHONY FAUCI, National Institute of Allergy and Infectious Diseases: That is correct. And that is the reason why there is such an important push going on domestically and internationally, where most of the cases are, to get people into a treatment regimen, because what's become clear over the past couple of years, that despite those daunting statistics, that when you treat people, identify people who are HIV-infected, you not only give them lifesaving therapy, but you dramatically diminish the likelihood that they will infect their sexual partners.

And so although the numbers are very high, we are now starting to go in the direction in several countries where the death rates are down, where the infection incidence is down, and where we're getting more people on therapy than we actually are getting newly infected. And we call that the tipping point.

And we're starting to see that in some countries. So the bad news is that it's still an immense epidemic/pandemic, but the good news is that we are clearly going in the right direction.

RAY SUAREZ:It's been 16 years since the combination therapies have really widely taken hold. Looking back over your shoulder, did it work better than you had even hoped back in 1996?

DR. ANTHONY FAUCI:Well, yes, yes. In many respects, Ray, it did work better, because we had been incrementally with newer drugs, one drug and then two drugs in combination, doing better and better.

But the idea of being able to suppress the virus to the point where you actually transform the life of an HIV-infected individual, where you have patients who otherwise would have died, who had been very, very debilitated essentially leading normal lives, and the statistics now are proving that to be the case, because we know now that if you put a young person in their mid-20s who is newly infected on these drugs in an appropriate combination, you can predict that they would live an additional 50 years to almost a normal life span.

I really—even though we were doing every day over decades, I really didn't imagine that we would have been this successful with having a combination that could do that. The real thing now is to implement that and get that to the people that need it. So that's really the challenge for the future.

Although the data are very encouraging, we still need to implement. And that's what we're talking about in World AIDS Day this year in 2012, that although we have accomplished a lot, we still have major challenges.

RAY SUAREZ:Your perspective is won the hard way, day by day over the decades. In the documentary "How to Survive the Plague," we see a shockingly young Tony Fauci, but we also see and are reminded of the terrible toll the early days of this disease took. Take us back to that time.

DR. ANTHONY FAUCI:Those are very dark years, Ray.

Before we had any therapy, it was like putting a Band-Aid on a hemorrhage. We had people who were presenting and not knowing that they were ill until they were far advanced in their illness.

My own personal experience was very dark and very depressing in many respects, although dealing with the patients gave me and them hope.

For example, in the mid-'80s, when I would be seeing patients here in the Washington area, that the median survival was six to eight months, which means that 50 percent of my patients would be dead in six to eight months. That was a terrible statistic and very painful for everyone involved.

And to have over the decades transformed into where we are now is an extraordinary accomplishment. And that's the reason why we are—we're energized because we have been so successful to make sure this gets very broadly implemented both domestically and internationally.

RAY SUAREZ:In one of the earliest publish pieces you wrote on the disease, before we even knew it was caused for sure by a virus, you wrote: "The mortality may well approach 100 percent, making this one of the most extraordinary transmissible diseases in history."

Even though the mortality is way down from 100 percent, is it that, one of the most extraordinary transmissible diseases in history?

DR. ANTHONY FAUCI:Oh, there is no doubt about that, Ray, that—by anybody's accounting, that if you look historically over centuries at the handful of diseases that have been public health disasters, the bubonic plague, the influenza pandemic of 1918, the smallpox pandemics, the measle pandemics, clearly, HIV-AIDS is in the very, very short list of one of the most devastating pandemics in the history of our civilization.

And that is not hyperbole. You look at the numbers, you look to see what has happened, and that is just the fact.

RAY SUAREZ:Right now, the big frontier seems to be lowering sexual transmission, because we have apparently caused great decreases in the mother-to-child in utero transmission. How come that is so much more stubborn?

DR. ANTHONY FAUCI:Well, it is sexual behavior, and it is very, very difficult when you have something that is so natural to the human species to get people to avoid risks.

I mean, for example, if you look here in the United States, the majority of cases are actually among men who have sex with men, particularly among the African-American population.

If you look internationally, where 90-plus percent of the cases are, male-to-female heterosexual transmissibility is the overwhelming modality of transmissibility.

As part of human nature, people take risks or even people don't even understand what the risks are. And that is a tough nut to crack when you are dealing with it.

That is the reason why educating and getting people to be tested, to identify whether they are infected or not and to counsel them if they are not infected and get them into a care treatment program if they are infected is so terribly important.

RAY SUAREZ:A lot of reasons to be encouraged and a lot of challenges ahead.

Dr. Anthony Fauci, thanks for joining us.

DR. ANTHONY FAUCI:You're quite welcome.

RAY SUAREZ:And, online, you can watch my interview with the director of the documentary we just mentioned, "How to Survive a Plague." Plus, we ask journalist Jon Cohen to take stock of the latest AIDS developments.