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Epidemiology and Social Science

Recruitment and Baseline Epidemiologic Profile of Participants in the First Phase 3 HIV Vaccine Efficacy Trial

Harro, Clayton D MD*; Judson, Franklyn N; Gorse, Geoffrey J; Mayer, Kenneth H§; Kostman, Jay R; Brown, Stephen J; Koblin, Beryl#; Marmor, Michael**; Bartholow, Bradford N††; Popovic, Vladimir‡‡for the VAX004 Study Group

Author Information
JAIDS Journal of Acquired Immune Deficiency Syndromes: November 1st, 2004 - Volume 37 - Issue 3 - p 1385-1392
doi: 10.1097/01.qai.0000122983.87519.b5


More than 30 HIV-1 vaccine candidates have been tested in more than 60 phase 1 and 2 trials since 1987.1 Preparations for phase 3 efficacy trials included epidemiologic, social, and behavioral studies of high-risk groups to determine the incidence of HIV infection and the feasibility of HIV vaccine efficacy trials.2–10 These studies indicated that efficacy trials were feasible but would have to address a wide range of challenges. Some of these challenges were related to scientific and epidemiologic issues such as the broad genetic variability of HIV-1, divergent modes of HIV-1 transmission, inadequacy of available animal models, and lack of known correlates of protection.1,11–17 Equally formidable were the political and ethical conundrums that evolved along the way, such as the criteria for advancing HIV vaccine candidates to efficacy trials, insurance for trial-related injury, treatment of trial participants who become HIV-1 infected, and the prevention and management of trial-related social harms.2,18,19

In 1998, VaxGen, Inc., initiated the first phase 3 placebo-controlled, double-blind efficacy trial of a recombinant glycoprotein 120 (rgp120) vaccine in North America and Europe. In phase 1 and phase 2 trials, this vaccine seemed to be safe and highly immunogenic in humans, and it was protective in chimpanzee challenge experiments.20,21 The principal purpose of the phase 3 trial was to evaluate the magnitude and breadth of rgp120 vaccine efficacy for preventing or modifying HIV infection in humans.

We describe recruitment, motivations for participation, demographics, and baseline risk factors and HIV status of trial participants.


Trial Design

This study (VAX004) was a randomized, double-blind, placebo-controlled, multicenter phase 3 trial to test an rgp120 vaccine containing 2 subtype B antigens (MN and GNE8) in preventing or modifying HIV-1 infection. It was designed to enroll 5000 men who have sex with men (MSM) and 300 women at heterosexual risk for HIV (WAHR). The sample size was based on anticipated annual HIV incidence of 1.5% in a similar population. Volunteers were randomly assigned in a 2:1 ratio to receive intramuscular injections of the vaccine formulated as 300 μg MN rgp120/HIV-1 combined with 300 μg GNE8 rgp120/HIV-1 and 600 μg alum adjuvant (AIDSVAX B/B) or placebo (600 μg alum adjuvant). Initial priming immunizations were administered at 0, 1, and 6 months, and boosters were given at 12, 18, 24, and 30 months. Subjects who remained noninfected were followed for 36 months after enrollment and were tested for HIV-1 infection at semiannual clinic visits. Subjects who became HIV-1 infected during the study were followed for 24 months after infection was confirmed. The primary objective was to evaluate the prevention of HIV-1 infection. Two secondary objectives were to modify HIV disease progression by preventing or reducing viremia and to assess vaccine safety. Other objectives were to identify the social and behavioral factors associated with trial participation, the immune correlates of protection, and the characteristics of infecting viruses.

Site Selection

Sites were selected on the basis of their access to HIV-negative populations at risk for sexually transmitted HIV-1, their ability to mobilize these populations for trial participation, and their capacity to conduct the trial according to Good Clinical Practices.22 The recruitment of high-risk women was limited to a small number of qualified sites.

Enrollment Criteria

Healthy MSM and women age 18 to 60 years who were not known to be HIV-1 infected but who were at risk for HIV-1 infection through sexual activity were screened for participation. To be eligible, men and women had to have a negative HIV-1 test result by enzyme immunoassay (EIA) within 30 days preceding the first immunization, be able to maintain study commitments for 36 months, and agree to practice effective birth control and abstain from conception until 3 months after their study participation ended. Men were eligible if they reported having had anal intercourse during the 12 months preceding the first immunization (excluding men in continuous monogamous sexual relationships of ≥12 months with a seronegative male partner). Women were eligible if they met at least 1 of the following criteria for the 12 months preceding the first immunization: (1) smoked crack cocaine, (2) exchanged sex for drugs or money, (3) had ≥5 male sex partners, or (4) had sexual intercourse with an HIV-1-infected man during the 30 days before the first immunization. Potential subjects were excluded from participation if they had a history of immunosuppressive disease or had injected drugs during the previous 3 years. Self-reports of past or ongoing chronic medical conditions were recorded at enrollment.

Ethical Considerations

The study was conducted in accordance with the Declaration of Helsinki, WHO guidelines, local institutional review board (IRB) ethical requirements, and with approval from regulatory authorities in each country. All sites obtained IRB approval of the study protocol and the informed consent form. Before enrollment, a detailed discussion of the following was required: (1) medical risks associated with participation; (2) no assumption of vaccine receipt or protection; (3) avoidance of behaviors that could lead to HIV infection; (4) understanding that volunteers who became HIV-infected during the trial would be referred for care, but that treatment or reimbursement for treatment-related costs would not be provided; (5) possibility of discrimination because other persons might assume that the volunteers were HIV infected or were engaging in stigmatized behavior; (6) possibility that the vaccine might induce a false-positive HIV-1 EIA result; and (7) hypothetic possibility of enhancement of HIV disease in vaccine recipients who later became infected.

Recruitment and Screening

Site-specific recruitment plans included a variety of recruitment methods. All recruitment materials were reviewed and approved by the study sponsor and local IRBs before implementation. Potential volunteers were prescreened by telephone or in person. Those who were HIV negative or of unknown HIV status and seemed to be eligible signed an informed consent form and were screened for study eligibility. Eligible subjects were enrolled within 30 days of screening. Reasons for nonparticipation or ineligibility (“screening failures”) were documented. At the end of enrollment, the study sponsor sent a questionnaire to each site to ascertain the most successful recruitment strategies. A standardized questionnaire about motivations for trial participation was administered to all subjects at enrollment. The motivations included altruistic (helping find a vaccine or helping one’s community) and nonaltruistic categories (receiving money, HIV testing and counseling, medical care and tests for diseases other than HIV infection, gaining protection against HIV from the vaccine, and being motivated to avoid risky behavior).

Diagnosis of HIV-1 Infection at Baseline

HIV status at screening and enrollment was determined by standard HIV-1 EIA (Abbott HIV-1 EIA; Abbott Laboratories, Abbott Park, IL) and confirmatory immunoblot (Novapath HIV-1 Immunoblot; Bio-Rad, Hercules, CA) assays conducted by a central laboratory (North America: Specialty Laboratories, Santa Monica, CA; Europe: Interlab, Heidelberg, Germany). To identify subjects who were infected (viremic) but HIV seronegative at enrollment, baseline sera from those who seroconverted within 6 months after enrollment were tested by “lookback” using the highly sensitive and specific HIV-1 nucleic acid test (NAT; Procleix HIV-1 Discriminatory Assay; Gen-Probe, Inc., San Diego, Ca).23–25

Risk Assessment

Risk factors for HIV infection during the previous 6 months, including sexual activity, drug use, and sexually transmitted diseases (STDs), were assessed by the use of an interviewer-administered standardized questionnaire. Comprehensive education, pretest, posttest, and risk reduction counseling were provided, according to a standard operational protocol, by trained counselors at every study visit.

Data Analysis

Data were analyzed using Statistical Analysis Software (SAS), version 8.1 (SAS Institute, Inc., Cary, NC).



Volunteers were recruited from June 1998 through October 1999 at 61 sites in the United States (n = 57), Canada (n = 3), and The Netherlands (n = 1; Fig. 1). More than two thirds of study sites were university research centers and community health clinics; one third were private medical clinics and clinical research organizations. The opening of the sites was staggered: Approximately half (29 of 61) of the sites began recruiting during the first 6 months of the study, and the remaining half (32 of 61) began recruiting during the following 6 months (Fig. 2). The addition of sites coincided with intensified recruitment efforts at already open sites and resulted in increased monthly enrollment from 5 subjects per site (Q1’99) to 10 subjects per site (Q3’99). The study was fully enrolled 17 months after initiation. There was wide variability in the number of participants per site (median, 87; range, 8–306).

VAX004 study sites.
Activation of sites and enrollment over time.

Most of the sites (75%) responded to the survey about recruitment methods. The most successful recruitment strategies were (1) direct recruiting at gay venues; (2) site-created advertising in gay and other local media; (3) study coverage in local and national television news; (4) passive distribution at gay venues of flyers, palm cards, or giveaways bearing information about the study and the site; and (5) referrals from participants. Other effective strategies were recruiting from a site’s established cohorts, using gay male staff as recruiters, and VaxGen-sponsored advertising campaigns. Less effective methods were posters in health clinics, referrals from physicians or public health facilities, community forums, “snowball parties,” and billboards.


Overall, 7185 persons were screened for eligibility at study sites. By 14 days (median) after screening, 5417 volunteers were enrolled. Of the total screened, 24.6% were ineligible (including 161 [2.2%] who tested as HIV-1 infected at screening) or chose not to participate. This does not include persons who knew they were HIV infected and were excluded at prescreening. Of the 1768 volunteers who were screened but did not enroll, 73.2% were eligible and 26.8% were ineligible for the study. For eligible volunteers, the main reasons for nonenrollment were loss to follow-up (54.6% of not enrolled); inability to commit to 3-year study (6.7%); enrollment closed (3.5%); negative reaction from partner, family, or friends (2.8%); concerns about false-positive HIV test result (2.4%); concerns about side effects (1.9%); fear of getting HIV from the vaccine (0.6%); waiting for a “better vaccine” (0.5%); and concerns about confidentiality (0.2%). Main reasons for ineligibility were HIV infection at screening (9.1% of not enrolled), history of immunosuppressive or other serious diseases (8.4%), not meeting the behavioral risk criteria (8.0%), and injection drug use during the past 3 years (1.4%).

Nearly all participants reported altruistic motivations for participation, including helping to find an HIV vaccine (98.8%) and helping their community (97.7%). However, some volunteers reported nonaltruistic motivations as well. Close to one half of volunteers (45.7%) reported a possible protection against HIV as a motivation for participation.

At baseline, most subjects (79.8%) reported past or ongoing clinically significant medical conditions. Of particular interest, 19.5% of MSM and 23.3% of women reported having received medical attention for depression. Other than allergies (23.2%), depression was the most commonly reported preexisting medical condition.


A total of 5108 men (94.3% of all volunteers) and 309 women (5.7%) were enrolled in the trial. The men were predominantly white, young, and well educated; the women were predominantly of races/ethnicities other than white, slightly older, and less educated (Table 1).

Table 1
Table 1:
Baseline Demographics of Study Participants

Diagnosis of HIV-1 Infection at Baseline

Of the volunteers who seroconverted (EIA+ and IB+) within 6 months after enrollment (serum specimens collected immediately before the first immunization), 14 were HIV-1 viremic by the NAT assay. Of these, 12 were viremic but antibody negative (NAT+ but EIA–), and 2 were viremic and antibody positive (1 NAT+ and EIA+ but IB–; 1 NAT+ and EIA+ and IB indeterminate).

Risk Factors

Overall, participants reported a high level of risk behavior during the 6 months preceding enrollment (Table 2). More than one half of men reported having ≥5 male sex partners, and nearly one third reported at least 10 partners. Unprotected anal sex with a male partner was reported by more than one half of MSM (57.5%). The HIV status of a substantial proportion of these partners was HIV positive or unknown (18.6% and 26.9% of MSM respectively). The proportion of men who reported unprotected insertive anal sex (46.8%) was larger than the proportion who reported unprotected receptive anal sex (36.5%). The women, compared with the men, reported fewer male sex partners during the past 6 months (median, 2 partners). More than one half the women reported unprotected vaginal sex (55.3%), including unprotected sex with partners who were HIV positive (15.9%) or of unknown HIV status (24.6%). Unprotected oral sex was reported by 42.9% of the men and 38.2% of the women.

Table 2
Table 2:
Risk Behavior During 6 Months Before Enrollment

More than one half of men and women reported drug use (noninjection) during the 6 months before enrollment (Table 2). The drugs most commonly used by MSM were poppers (32.6%), hallucinogens (13.6%), and enhancers of sexual performance (12.7%). The drugs most commonly used by the women were crack cocaine (47.9%) and snorted cocaine or heroin (30.4%). STDs were self-reported by 14.5% of the men and 13.6% of the women. Among the men, the most common STD was gonorrhea (anal, genital or oral); among the women, the most common STD was chlamydial infection (genital or anal).

High-risk factors, defined as 2 or more of the specified behaviors during the 6 months before enrollment (10 or more sex partners, unprotected receptive sex, 1 or more HIV-positive partners, any STD, or 2 or more “party drugs” [poppers, cocaine or heroin, hallucinogen, amphetamines, enhancers of sexual performance]), were reported by 55.6% of men and 58.3% of women. All 14 volunteers with a diagnosis of HIV infection at enrollment reported high-risk factors.


The successful enrollment for the world’s first phase 3 efficacy trial of a preventive HIV-1 vaccine was a landmark public health event. In the years preceding the trial, some foundation had been laid in that several sites had gained experience recruiting at-risk persons for willingness-to-participate and vaccine-preparedness studies.3–9,26 Although these studies provided valuable insights regarding recruitment and enrollment, all of them were conducted in the context of hypothetical HIV vaccines. A handful of other sites had experience conducting small phase 1 and 2 trials of candidate HIV vaccines. The resources and the effort needed to conduct large-scale phase 3 trials were not known. Ultimately, it took the mobilization and expertise of 61 sites to achieve the enrollment goal in 17 months.

Before the VAX004 study, only a few sites had well-established community education programs. Community knowledge of preventive vaccines in general, and HIV vaccines in particular, was minimal at most of the sites. Therefore, along with establishing clinical trial capacity, most sites faced the simultaneous challenge of developing community awareness from the ground up. Sites that were able to establish efficiently the capacity for a large-scale trial and develop community awareness of HIV vaccines excelled at enrollment.

The widely differing recruitment strategies were site specific and depended to a large extent on the creativity, ingenuity, and resourcefulness of site staff. At some sites, local approaches were supplemented with VaxGen-sponsored events or media campaigns. During the second half of the recruitment period, site proliferation and activation converged, and awareness of the VAX004 study in at-risk communities led to exponential enrollment (Fig. 2). At the end, many sites reported that the number of eligible volunteers who were willing to participate exceeded the number of enrollment slots.27 Developing research instruments that capture information on how sites implement a trial and expand community and participant awareness of a trial are important considerations for future studies.

The ratio of persons screened to persons enrolled was low. Once the men and women reached a point at which they were willing to sign a consent form and undergo screening for the study, it was unusual for them to decide not to participate or to be found ineligible. Recruitment approaches and community awareness efforts were concentrated on the main eligibility criteria. In addition, many sites implemented extensive prescreening to exclude persons who were obviously ineligible. This prescreening saved time and labor for the staff of the study sites and for the sponsor.

Despite considerable effort to achieve greater demographic diversity in the study cohort, most of the volunteers were educated, white MSM. Because few of the sites had expertise in recruiting MSM of races/ethnicities other than white and WAHR, these populations were underrepresented. These data are consistent with those reported from willingness-to-participate studies conducted during the past decade.3,4,7,10,26 However, this lack of demographic diversity is incongruent with current epidemiologic trends in North America, and portends new challenges for future trials and, when an effective vaccine is licensed, for the utilization of that vaccine.

Altruistic motivations were unanimously endorsed by men and women as reasons for enrolling in the trial. However, nearly one half the volunteers thought the vaccine might offer some protection from infection. These data underscore the need for continued counseling in HIV vaccine trials, reminding volunteers not to assume that they will receive the vaccine or that it will protect them against HIV infection.

Medical histories obtained at baseline revealed a large proportion of subjects with past or ongoing depression. This finding confirms the findings of earlier willingness-to-participate studies that reported an association between depression and sexual risk taking among MSM,28 as well as an association between depression and willingness to participate in an HIV vaccine efficacy trial.29 The prevalence of depression among participants in this trial presented challenges for the affected subjects and for the study staff, particularly in the efforts of staff to maintain a high level of study compliance. It also highlights the importance of preparing for the psychologic needs of participants in future efficacy trials involving MSM and women at high risk for HIV infection.

The recent development of the NAT assay enabled the identification of HIV-infected volunteers during the preseroconversion window at the time of enrollment. Knowing that these infections occurred before the first immunization allowed researchers to exclude these persons from the measurement of HIV incidence during the study and provided greater precision to the vaccine efficacy analysis.

The prevalence of HIV infection at screening (2.2%) was not representative of true HIV prevalence among MSM and WAHR because the trial sought to enroll persons who were not infected. Most of those who were found to be HIV infected had been unaware of their HIV status before screening. It is likely that the true prevalence of HIV infection among these populations was higher. Recent reports of high HIV prevalence among young MSM in 7 major US cities, and the fact that only a small proportion knew they were infected, support these observations.30,31

Overall, the trial sites were able to enroll a cohort at high risk for sexually transmitted HIV infection. High risk was evidenced by the substantial proportion of men and women who reported high numbers of sex partners, unprotected sex with partners who were known to be HIV positive and partners of unknown HIV status, and the high prevalence of STDs and drug use (noninjection) during the 6 months preceding enrollment. This was consistent with data from willingness-to-participate studies and recent reports of high STD prevalence among MSM and women at high risk.4,5,7,28,32 These data demonstrate the willingness of persons at high risk to enroll in HIV vaccine efficacy trials, the importance of ongoing HIV risk reduction counseling, and the urgent need for an HIV vaccine.


The successful recruitment for this study was a milestone in the development of safe, effective AIDS vaccines. Essential questions about the feasibility and the conduct of HIV-1 vaccine field trials within high-risk MSM and WAHR have been answered. Beyond determination of rgp120 HIV vaccine efficacy, this trial will provide other valuable data, including HIV incidence rates and associated risk behaviors among MSM and WAHR over time, HIV genetic variability throughout North America, and dynamics of antiretroviral therapy utilization and associated HIV drug resistance. These data and other lessons learned from this trial will pave the way for the clinical development of the next generation of HIV-1 vaccines and will open avenues of research for future efficacy trials.


The authors thank the VAX004 Study Group, site investigators: Franklyn Judson, MD, Denver Department of Public Health, Denver, CO; Geoffrey J. Gorse, MD, Saint Louis University, St. Louis, MO; Clayton D. Harro, MD, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD; Kenneth Mayer, MD, Fenway Community Health, Boston, MA; Jay Kostman, MD, Philadelphia Fight, Philadelphia, PA; Harold Kessler, MD, Chicago Center for Clinical Research, Chicago, IL; Stephen J. Brown, MD, AIDS Research Alliance, West Hollywood, CA; Richard DiCarlo, MD, Louisiana State University Health Sciences Center, New Orleans, LA; Michael C. Keefer, MD, University of Rochester, Rochester, NY; Bienvenido G. Yangco, MD, Infectious Disease Research Institute, Inc., Tampa, FL; Javier O. Morales, MD, Clinical Research Puerto Rico, Inc., San Juan, PR; Donald Forthal, MD, University of California at Irvine Medical Center, Orange, CA; Susan Buchbinder, MD, San Francisco Department of Public Health, San Francisco, CA; Connie Celum, MD, University of Washington/Seattle HPTU, Seattle, WA; Keith Henry, MD, Hennepin County Medical Center, Minneapolis, MN; Jeffrey M. Jacobson, MD, Beth Israel Medical Center, New York, NY; Jerry Cade, MD, Wellness Center, Las Vegas, NV; Elaine Thomas, MD, University of New Mexico Health Sciences Center, Albuquerque, NM; Richard Novak, MD, University of Illinois at Chicago, Chicago, IL; Frank Rhame, MD, Abbott Northwestern Hospital, Minneapolis, MN; Ralph W. Richter, MD, Clinical Pharmaceutical Trials, Inc., Tulsa, OK; Michael C. Caldwell, MD, Dutchess County Department of Health, Poughkeepsie, NY; Beryl Koblin, PhD, New York Blood Center, New York, NY; Michael Marmor, PhD, NYU School of Medicine, New York, NY; Catherine Creticos, MD, Howard Brown Health Center, Chicago, IL; Michael Para, MD, Ohio State University, Columbus, OH; Stephen K. Tyring, MD, UTMB Center for Clinical Studies, Houston, TX; David McKinsey, MD, Antibiotic Research Associates, Kansas City, MO; Neil Flynn, MD, University of California at Davis Medical Center, Infectious Diseases, Sacramento, CA; Edwin DeJesus, MD, IDC Research Initiative, Altamonte Springs, FL; Steven Santiago, MD, Care Resource, Inc., Coral Gables, FL; Barry M. Miskin, MD, Palm Beach Research Center, West Palm Beach, FL; Cecilia Shikuma, MD, Hawaii AIDS Clinical Trials Unit, Honolulu, HI; Melanie Thompson, MD, AIDS Research Consortium of Atlanta, Atlanta, GA; James O. Kahn, MD, UCSF-Positive Health Program, San Francisco, CA; Ross G. Hewitt, MD, Erie County Medical Center, Buffalo, NY; Michael S. Somero, MD, Office of Michael S. Somero, MD, Palm Springs, CA; Roel A. Coutinho, MD, GG&GD/Municipal Health Service Amsterdam, Amsterdam, The Netherlands; Martin Fenstersheib, MD, Crane Center, San Jose, CA; M. Angeli Adamczyk, MD, ACRC/Arizona Clinical Research Center, Inc., Tucson, AZ; Peter Piliero, MD, Albany Medical College, Albany, NY; Ronald Poblete, MD, North Jersey Community Research Initiative, Newark, NJ; Michael Sands, MD, University of Florida at Jacksonville, Jacksonville, FL; Barbara Gripshover, MD, University Hospitals of Cleveland, Cleveland, OH; David Brand, MD, North Texas Center for AIDS & Clinical Research, Dallas, TX; Patrick Daly, MD, Nelson–Tebedo Health Resource Center, Dallas, TX; Mark J. Mulligan, MD, University of Alabama at Birmingham, Birmingham, AL; Robert L. Baker, MD, Community Medical Research Institute, Indianapolis, IN; Peter S. Vrooman, Jr., MD, ALL TRIALS Clinical Research, Winston–Salem, NC; Robert Hogg, PhD, BC Centre for Excellence in HIV/AIDS, Vancouver, BC, Canada; Jean Vincelette, MD, Hospital Saint-Luc du CHUM, Montreal, PQ, Canada; Brian P. Buggy, MD, Wisconsin AIDS Research Consortium, Milwaukee, WI; James H. Sampson, MD, Research & Education Group, Portland, OR; Sharon Riddler, MD, University of Pittsburgh, Pittsburgh, PA; Robert A. Myers, MD, Body Positive, Inc., Phoenix, AZ; Michelle Lally, MD, The Miriam Hospital, Providence, RI; Joseph Jemsek, MD, Jemsek Clinic, Huntersville, NC; Howard Grossman, MD, Polaris Medical Group, New York, NY; and Ken Logue, MD, CascAids Research, Toronto, ON, Canada.

The authors especially thank all VAX004 trial volunteers for their participation and commitment, and the staff at the trial sites for their dedication and perseverance to this trial. The authors also thank Tom Porter, John Jermano, John Curd, Marlene Chernow, Gina Alonzo, Lisa Stoll, Nicole Lynch, Nzeera Ketter, and the VaxGen and ProTrials site monitors for their contribution to trial recruitment. They are grateful to Bill Heyward and Marc Gurwith for their support and review of the manuscript.


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rgp120 HIV vaccine; efficacy trial; HIV incidence; risk factors; AIDSVAX B/B

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