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FARAI CHIDEYA, host:

From NPR News, this is NEWS & NOTES. I'm Farai Chideya.

On yesterday's show, we explored controversial new research about how AIDS traveled to the United States. Today, news about what was a promising AIDS vaccine. Until recently, scientists had high hopes for a vaccine made by the pharmaceutical giant Merck. Then, researchers learned that some who got that vaccine still got the AIDS virus. The clinical trials have been halted, subjects are learning whether they were given the vaccine or a placebo, and scientists are trying to figure out what went wrong.

Soon, we'll hear what this means for communities at high risk for AIDS. But first, we speak with NPR science correspondent Brenda Wilson. Brenda, welcome.

BRENDA WILSON: Thank you.

CHIDEYA: So, can you tell us more about the vaccine that was being tested?

WILSON: Well, it had shown great promise in the laboratories. The vaccine was constructed of elements of the virus that had been disabled, so that in fact it could not cause HIV, and also included a cold virus at no - and it was combined. And when they injected blood cells in test tubes with this vaccine, you know, the blood cells attacked HIV. But it turned out that when they started testing them in humans as early as September, Merck said, okay, they called a halt because it was clear people were becoming infected, and people who got the vaccine, and people who got the placebo, of course. But people who got the vaccine were becoming infected.

CHIDEYA: Were they becoming infected at higher rates than the placebo group?

WILSON: Yes. I mean, that was what they subsequently found out when they - examined the data. It - in the Americas, where the trial has been underway since, I guess, 2004, they had up to 49 people who had gotten the vaccine, who became infected, compared to 33 people who got the placebo. And then, when you look at a subset of that, 21 people who got the vaccine had a high immunity to the cold virus, which was really, you know, raised a lot of questions. It was almost twice as many people who had a high immunity to the cold virus.

CHIDEYA: That's significant because the cold virus was used as part of making the vaccine. Was that counterintuitive to the scientists?

WILSON: Anything that they say is only speculative. They really don't know what may have happened. But one of the theories is that, perhaps, the vaccine stimulated the immune system in the wrong way. So, that by increasing the number of CD4 or helper cells, cells which attack foreign bodies when they enter the body, may have in fact provided targets for HIV, which made people much more susceptible to being infected.

CHIDEYA: It's my understanding that none of the people in the South African group who participated in the test were told whether they got the vaccine or the placebo.

WILSON: You're very seldom, in any sort of clinical experiment, told whether you got the medicine or not, because being told whether you got something can sometimes change the way you behave. People who think they got the vaccine, which is one of the questions they have to ask here in looking at the higher rates of infection - did people figure out in the Americas, as well as in South Africa that they have gotten the vaccine because, you know, when you got a vaccine, you can get really very sort(ph) spot.

So, there is some, you know, it's possible that people speculated that they in fact got the vaccine and were safer, even though people in clinical experiments like this are counseled that there's no way of knowing that there are potential risks. But human nature, being what it is, people still - you know, you can never predict how people are going to behave. So, they're not told when they're given the medicine, and that's why you also have sort of a control group as well.

CHIDEYA: So, how might this affect research around AIDS vaccines, even around prevention?

WILSON: I think it's going to slow it down, but Dr. Anthony Fauci at the National Institute of Allergy and Infectious Diseases says that it won't stop investigations of AIDS vaccines. There are some that are underway that will have to be, you know, stopped until they've determined what happened, and that could take a long time. But then, vaccines that do not use the cold virus, for example - it is possible that they can continue with those kinds of investigations.

CHIDEYA: Well, Brenda, thanks so much.

WILSON: Thank you.

That was NPR science correspondent Brenda Wilson.

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