Vaccines are considerably more popular than vaccine tests. A survey released this month by the HIV Vaccine Communications Campaign found that, while most Americans believe vaccines are the best hope for stemming the AIDS epidemic, a majority would be reluctant to support a loved one or family member participating in a clinical test. Yet you can"t have a vaccine without a vaccine test.

Today, the University of Pennsylvania has a vaccine that may or may not prevent the transmission of HIV. Developed by Merck, which has given it the catchy name "Ad5 HIV-1 gag/pol/nef," the vaccine uses an inactivated common cold virus to carry non-reproducing synthesized HIV genes into the body. This, in theory, will enable the immune system to recognize HIV and develop a response to it. Early tests have shown the approach to be both safe (you cannot get HIV from the vaccine) and promising. Penn"s job, along with agencies in 12 other U.S. cities, Puerto Rico, and five foreign countries, is to test the vaccine on a large scale, as part of what organizers are calling the Step Study.

To do this, participating agencies will need to vaccinate people who will subsequently come in contact with the HIV virus — but, of course, they can"t give anyone HIV. The study"s solution to this problem is to give the vaccine to "high-risk" populations. For the University of Washington, in Seattle, that means gay men; for the HIV Vaccine Trials Unit at Penn, it means black women in West and Southwest Philadelphia — one of the fastest growing infected populations in an area with one of the nation"s highest rates of infection.

The particular black women Penn seeks are those who engage in high-risk behavior: intravenous drug users, prostitutes or people with HIV-positive partners — women who, in many cases, distrust institutions. So, Penn has its work cut out for it. It needs to haul its Ivy League self out into West Philly and find these high-risk women. It needs to earn their trust. And most of all, it needs to do so ethically, without encouraging the very behavior that the study depends on.

It starts with "the condom ladies."

Jenny Freeman and Alex, who asked that her last name be withheld, are Penn graduate students who serve as scouts for the Step Study. They seek out the "risk pockets" where one would be likely to find drug users or prostitutes.

"Our job is to go to the worst neighborhoods and talk to the people you"re supposed to cross the street to avoid," explains Freeman. The two women were selected because of community service work they had done in the past and are on a paid contract.

Their search often begins with a tip from a participant in a previous study, something like, "When I turn tricks, I go to intersection X." The scouts will go to the intersection, dig through the trash and walk around in search of telltale signs. Because they"re so conspicuous (both are white), they assume the identities of outreach workers, carrying and distributing condoms.

"The outreach model is recognizable," says Alex. "It"s a way to explain two white girls, and an ethical imperative."

"We think of the condoms like our calling card," Freeman adds.

The condom ladies gather as much information as they can about each area. Learning the price for oral sex, for example (anywhere from $3 to $60), gives them a sense of the local economy, which helps Penn determine the rate of compensation for study participants (Penn doesn"t want pay to be inadequate, the scouts say, but it also doesn"t want the compensation to be "coercive" — so high that people can"t afford to turn it down). In pursuit of such information, the condom ladies have crawled into crack houses, sat at go-go bars and stood on corners amongst drug dealers, who, they say, have been especially protective of them. They recall one incident where a young dealer tried to hassle them and was banished by his superiors to a less desirable corner.

In a single conversation, Alex says five times that the guiding principle of her scouting is "respect."

"We try not to take a moral position on any behavior," she says. Other than the condoms, the only way the women interfere with the risk pockets is by dropping the idea of the vaccine in the community"s collective head. They don"t want to advertise the study, they say, but work to assuage common concerns such as the idea that the vaccine can give someone HIV.

Once this reconnaissance is done, Penn dispatches its "mobile unit" — an RV with a university logo — to interview potential volunteers. The coordinator for these outings is Tiffany Brown, a young black woman with a background in youth organizing. Brown"s recruitment strategy is essentially to put up fliers announcing the van"s presence and the availability of compensation. Then, she waits.

"People come to us," she says.

Penn asked City Paper not to track down the van, for fear that publicity might deter potential participants. But Lora, a thin, angular white woman who participated in a 1992 Penn HIV-vaccine trial, explains why she enrolled.

"It was for the money," she says in a smokey voice. "I was a junkie. When you"re using, you live to use."

Once Lora was drawn in, however, she got enamored of the idea that she was helping people. It was a position, she says, that junkies rarely get to be in.

The van interviews last approximately 30 minutes, and include informed consent, health background (including HIV status), questions about high-risk behavior and culling extensive contact information.

"Finding people is key for me," says Brown. "High-risk" people tend to be transitory, and often prefer to fly below the radar of forwarding addresses and registrations. So interviewers ask not just for phone numbers, but for non-traditional information such as regular haunts.

News of the easy-money opportunity spreads quickly and Brown says she usually has people lined up outside the van. Thus far, her team has screened nearly 130 people, and 93 appear to be eligible. Once they get up to 150 eligible participants, Penn will be ready to start testing the vaccine.

The trial will work like this: The names of all the approximately 3,000 worldwide participants will be entered into a database. The computer will randomize the names and assign the vaccine to half of them, and a placebo to the others. Beginning in September, a nurse at each site will administer the injections. The volunteers will not be told which injection they received.

Brown says that thus far, only one interviewee has asked her "the question" — can she be guaranteed the vaccine? (She can"t.) But Brown"s emphasis highlights a central concern for the study: That participants will assume the vaccine works.

The researchers say they don"t want to encourage high-risk behavior, so they emphasize to participants that there is a 50 percent chance they"re being injected with an inactive substance, and that even if they get the vaccine, no one knows how well it works. They also plan to flood participants with "risk-reduction counseling."

It"s impossible to assess how aggressively Penn follows through with this counseling. But Lora, the participant in the 1992 trial, says that the risk-reduction counseling she received was anything but subtle.

"Oh, my God, I wanted to smack them," she recalls. "I was like, "Come on, I"m not stupid, I heard you.""

In fact, the counseling worked for Lora. She has stopped using and now sits on Penn"s community advisory board. Hers is a success story, but it highlights another difficulty for Penn: The research team is discouraging behaviors that, in reality, they need people to engage in. What if all the prevention education works?

Throughout the study, says Debora Dunbar, the trial"s clinical coordinator, participants" behavior will be monitored and, in the event that the vaccine group partakes in more high-risk behavior than the placebo group, the analysts will take it into account. But, she adds, "if aggressively discouraging people worked, we wouldn"t need to do a vaccine study."

Penn"s HIV prevention unit is betting that its best prevention efforts will fail.

The Step Study will take approximately three years. According to Dr. Ian Frank, one of the primary investigators for Penn"s trial unit, success will be measured by comparing the rate of HIV contraction in the vaccine group to that in the placebo group. The researchers expect people in both groups to contract the virus, but for the vaccine group to contract it at a statistically significant lower rate; for example, says Dr. Frank, "if 50 people become infected, we think that 60 percent fewer people who became infected will be in the vaccine group."

The vaccine is also designed to help an infected person reduce her viral load, thereby delaying the progression of the virus. The Step Study anticipates that vaccinated people will see a statistically significant difference in viral load from the placebo group.

Should the vaccine work, a whole new set of ethical questions will be introduced. For now, though, the quandaries remain in the realm of testing. The study"s methodology has been reviewed by the FDA, the World Health Organization, and the Joint United Nations Programme on HIV/AIDS — it meets industry ethical standards. But ultimately, the meaning of ethics falls under the jurisdiction of the individual conscience: Are the Penn researchers comfortable with the study?

Faced with this question, team members express levels of comfort ranging from perfectly content to fairly ambivalent. The most conflicted is Alex, the condom lady, who worries about luring drug addicts into clinical research with even small amounts of money.

"Ten dollars is a lot more money to them than it is to me," she says.

But, she reasons, when it comes to the imperative of stopping HIV, "a vaccine is our best hope right now."

And you can't have a vaccine without a vaccine test.