AMNA NAWAZ: After years of work, there's been some progress in the fight against Alzheimer's disease, the incurable brain condition that affects more than six million Americans.

Several new drugs have shown small, but positive results in reducing the cognitive decline associated with the disease.

William Brangham has our look at the breakthroughs and what they could mean.

WILLIAM BRANGHAM: Earlier this month, an FDA advisory panel unanimously agreed that the drug known as Leqembi modestly slowed the progression of Alzheimer's.

The FDA is expected to give final approval next month.

A similar drug known as donanemab has also shown promise in clinical trials.

It too could see FDA approval as soon as this year.

The results from these drugs are modest, and there are concerns about certain side effects, like brain swelling and bleeding.

So, for more on these advances and what obstacles lie ahead, we're joined by Dr. Richard Hodes.

He's the longtime director of the National Institute on Aging at the National Institutes of Health.

Dr. Hodes, so good to have you on the program.

As you well know, researchers have been trying for decades to find some crack in Alzheimer's armor.

And now we have some hope with these new drugs.

When you look at the clinical results so far, how promising disease seem to you?

DR. RICHARD HODES, Director, National Institute on Aging: I think you have you have put it very well in context.

For the first time, this is a set of results which, in the analysis of experts who review the findings, is a clear, significant impact on slowing the course of disease.

Where there is discussion is the magnitude of this change.

But where I think we would all agree is that this is an important first step that holds promise of improving by working upon this foundational initial finding to do even better and get a better ratio, if you will, of positive effect, of prevention treatment, and to side effects, which are also a significant point of data in these findings and in the recommendations that are forthcoming from them.

WILLIAM BRANGHAM: You mentioned this here, that these drugs seem to slow the progress of the disease.

Explain why that is significant.

DR. RICHARD HODES: Yes, well, Alzheimer's disease is -- we recognize now is a slowly progressive disease, so that the findings of abnormalities in the brain actually begin years, even decades before the appearance of symptoms.

And then there's slow progression.

It varies from individual to individual.

So, in effect, if these treatments were capable of not totally reversing or curing the disease, but slowing it to a point where people retain their function, their ability to be independent, interact with families, to have meaningful life of high quality, this would indeed be an important outcome of the treatment.

WILLIAM BRANGHAM: You mentioned this issue of the side effects.

And I know there's this ongoing debate about whether Medicare should cover these treatments, given the comparison of benefits to the side effects.

How do you weigh those side effects, in comparison to the benefits?

DR. RICHARD HODES: What I think we need to do in research going forward is to understand which individuals are most likely to profit from the treatment, which individuals are at higher risk.

And this information provides a basis then for patients, families and their care providers to make an individualized judgment about the cost/risk benefit for any individual case.

In the meantime, it's going to be important for us to conduct research to better identify, who are the best candidates?

Who are least likely to have the adverse effects?

And this kind of research is already ongoing.

WILLIAM BRANGHAM: There are still so many questions and mysteries about this disease and who gets it and why we get it.

But we are learning more about risk factors and possible prevention.

What is the best knowledge on that front?

DR. RICHARD HODES: Very important.

So, in addition to looking for cures, treatments, the ability to intervene, to decrease risk, to prevent is enormously important.

A few years ago, NIH commissioned from the National Academies an analysis of what we knew about risk factors and what we knew about how we could reduce the risk of disease.

And the risk factors for which there was the best evidence that intervention could help were three identified at that point, one, control of blood pressure, the other, maintaining cognitive activity, and, third, physical activity.

Now, since the time of that report, one of them, blood pressure control, has been shown in a randomized clinical trial, this is the gold standard of a test for causal impact, that by more intensively controlling blood pressure in people in mid-age and older age, there was significant decrease in the appearance of lesions in the brain, which were seen in Alzheimer's disease, and a decrease in mild cognitive impairment.

That's a stage that often precedes dementia.

So this is as good as it gets, if you will, in terms of direct evidence that controlling blood pressure makes a different difference.

In the meantime, there are going -- ongoing trials to see whether controlling diet or physical activity or cognitive training will have a similar effect.

WILLIAM BRANGHAM: And you have also spoken about the need to increase the racial diversity amongst the people who we do research with.

Can you explain?

That may seem self-evident to you, but why is that so important?

DR. RICHARD HODES: Well, it's important that a couple of levels.

We can start with sort of the moral, ethical imperative, that we need to conduct research that has the opportunity to benefit all the people in our country and, for that, matter globally.

And to do so, we have to have inclusion of people with that kind of diversity in our clinical studies and trials.

And beyond that moral imperative, this is not just hypothetical.

We have very compelling findings to demonstrate that the risk that's imposed by a genetic variant in white, Caucasian, European descent does not have the same risk in an African American population.

There are differences, genetic, as well as in experience and life exposures, that mean that individuals of different parts of our population are likely to have different pathways to Alzheimer's disease, and so likely to benefit differentially from treatment.

We're only going to know that if we include a diverse population in our research studies.

WILLIAM BRANGHAM: All right, Dr. Richard Hodes, director of the National Institute on Aging, thank you so much for your time.

DR. RICHARD HODES: Thanks so much for the opportunity to speak with you.