Community preparedness for HIV vaccine trials in the Democratic Republic of Congo

This paper reports on an assessment of community preparedness for HIV vaccine trials in the Democratic Republic of Congo. Formative research was conducted in the capital city of Kinshasa during the period October 2003 to March 2004 to answer questions pertinent to planning trials of a preventive HIV vaccine and to identify related issues. Twenty‐seven in‐depth interviews and two focus groups were held with potential trial participants and community leaders. Data was collected on the subjects of vaccines, HIV/AIDS and sexual behaviour, and an HIV vaccine. The study also sought to identify factors that motivate a person to volunteer for a vaccine trial or which are disincentives to participation, along with preparedness of the larger community for trials. Personal concerns for health and for the impact of the epidemic on families and country were common motivations for participation. The danger of an experimental vaccine and the stigma of a positive HIV antibody test as the result of vaccination are major concerns and disincentives. The health, educational, and local non‐governmental sectors are identified as having important roles to play in assuring preparedness for trials, although significant challenges exist to achieving community preparedness.

Résumé

Cet article est le compte‐rendu d'une évaluation de la disposition communautaire vis‐à‐vis des essais de vaccin anti‐HIV en République Démocratique du Congo. Un programme de recherche et de formation fut entrepris dans la ville de Kinshasa, la capitale, d'octobre 2003 à mars 2004 afin de répondre aux questions concernant un projet d'essais d'un vaccin préventif anti‐HIV et d'identifier d'éventuels problèmes annexes. Vingt‐sept entretiens approfondis et deux groupes de discussion furent mis en place réunissant des participants potentiels à ces essais et des dirigeants communautaires. Des données furent recueillies à propos des vaccins, du HIV/sida et le comportement sexuel, et d'un vaccin anti‐HIV. L'investigation cherchait également à identifier les facteurs qui incitent quelqu'un à se porter volontaire pour un essai de vaccin ou qui ont un effet dissuasif à cet égard, ainsi qu'à préciser la disposition de la communauté au sens large à accueillir de tels essais. Les motifs les plus courants en faveur d'une participation sont le souci de l'individu pour sa propre santé et pour l'impact de l'épidémie sur la vie familiale et le pays. Les inquiétudes avec effet dissuasif portent sur le risque éventuel qu'implique un vaccin encore au stade expérimental et sur la honte engendrée par un résultat séropositif en raison des anticorps suite à la vaccination. L'étude fait ressortir le fait que les services de santé et d'éducation ainsi que les organismes locaux non gouvernementaux ont un rôle majeur à jouer pour promouvoir la disposition à participer dans de tels essais, bien que cet effort rencontre des résistances non négligeables au sein de la communauté.

Resumen

En este ensayo analizamos en qué medida está dispuesta la comunidad de la República Democrática del Congo a participar en ensayos para una vacuna contra el sida. De octubre de 2003 a marzo de 2004 se realizó una investigación formativa en la capital Kinshasa con el objetivo de obtener las respuestas a determinadas preguntas sobre la planificación de ensayos con una vacuna preventiva contra el sida e identificar temas relacionados. Se llevaron a cabo veintisiete entrevistas exhaustivas y dos grupos de discusión con posibles participantes en el ensayo y con líderes de la comunidad. Asimismo se recogieron datos sobre temas relacionados con las vacunas, el VIH y el sida, la conducta sexual y la vacuna contra el sida. La finalidad del estudio también fue identificar qué factores motivan a una persona a presentarse como voluntario para un ensayo de una vacuna o qué factores disuasivos les impiden participar. También se analizó en qué medida está la comunidad más numerosa dispuesta a participar en los ensayos. Algunas de las motivaciones más comunes para participar eran estar preocupados por la salud y el impacto de la epidemia en las familias y el país. Las principales inquietudes e impedimentos eran el peligro de una vacuna experimental y el estigma de dar positivo en la prueba de anticuerpos del VIH como resultado de la vacuna. Identificamos que los sectores sanitarios, educativos y no gubernamentales del municipio desempeñan un importante papel a la hora de asegurar que la población esté preparada para los ensayos, aunque existen aún escollos por superar si queremos conseguir que la comunidad esté preparada.     

Socioeconomic status and HIV vaccine preparedness studies in North America

Educational level, employment, and income are key components of socioeconomic status (SES). This article is a systematic review of SES variables in North American countries, and their relationship to willingness to participate (WTP) and retention in a hypothetical preventive phase 3 HIV vaccine trial and in actual HIV vaccine trials. Men who have sex with men (MSM) tended to have higher educational levels, be more employed, and had higher income levels than injection drug users (IDU) and women at heterosexual risk (WAHR). In large part, there was no relationship between educational level and WTP, as well as between educational level and retention. Similarly, there was no relationship between employment and WTP. In WAHR who were African-American, those employed were less likely than others to complete the study at 18 months. The exact occupations of participants analyzed have not been specified, and specification of these occupations may help determine whether enhanced retention (ER) strategies are required.     

Use of predictive markers of HIV disease progression in vaccine trials

Generating broadly neutralizing antibodies with candidate vaccines has remained an elusive goal. Consequently, vaccine candidates developed have aimed at eliciting cell-mediated immune effector activities (CMI) that could delay disease progression, and maybe also limit secondary transmission, by controlling virus replication. There is considerable discussion about what types of endpoints would constitute definable standardized clinical benefit to the individual that would result in licensure of these candidate vaccines. Identifying biomarkers that can be used as surrogates for clinical endpoints in randomized clinical trials would be useful, because it would shorten studies and reduce costs. Biological markers associated with disease progression and secondary transmission and that may be used as prognosis markers and surrogate endpoints in HIV vaccine trials have emerged from analyses of data from studies on natural history of HIV infection. Extensive literature is cited to support the use of plasma viral load as a primary endpoint for supporting licensure decisions. Overall, a significant result on viral load in a vaccine trial should be considered as a significant breakthrough for vaccines and be aggressively pursued with the caveat that such a result should rapidly be followed by well-defined studies to verify durable virological and immunological vaccine benefit, as well as ultimate clinical benefit. The review also provides perspectives on magnitude of viral load reduction, durability of viral load reduction for reduced progression of HIV disease.     

Representation of Latinos and Blacks in screening for and enrollment into preventive HIV vaccine trials in New York City

IntroductionIn the United States, Latinos and Blacks are disproportionately affected by HIV/AIDS, but have been underrepresented in HIV vaccine trials. We assessed screening and enrollment of Blacks and Latinos for preventive HIV vaccine trials conducted in New York City, 2009–2012.MethodsA retrospective analysis was conducted among 18–50 year old men and transgender women screening for four preventive phase 1 and 2 HIV vaccine trials. Demographic, recruitment, and behavioral/medical eligibility data and outcome of screening were examined. To determine factors associated with enrollment, a multivariable logistic regression analysis was performed.ResultsAmong 6077 individuals who provided contact information, 2536 completed a phone pre-screen. 96 (1.6% of recruitment contacts) enrolled. Latinos were 35.7% of recruitment contacts, but 17.7% of those enrolled, whereas Blacks were 22.5% and 32.3%, respectively. Among all Latinos, nearly one third were excluded for being uncircumcised, an eligibility criterion for several studies. In multivariable analysis among potentially eligible potential participants, controlling for age and recruitment method, Latinos were less likely than Whites to enroll in a preventive HIV vaccine trial (aOR 0.52, 95% CI 0.28–0.95) whereas Blacks were as likely as Whites (aOR 0.99, 95% CI 0.59–1.67). Individuals recruited through print advertisements, social media/internet, referral, and other modes were more likely to enroll compared to those recruited through in-person outreach, controlling for age and race/ethnicity.ConclusionsTargeted outreach has led to substantial inclusion of Latinos and Blacks, with Blacks comprising almost a third of those enrolled in these preventive HIV vaccine trials. Latinos, however, were less likely to enroll compared to Whites. Circumcision status as an eligibility criterion partly accounts for this, but further studies are warranted to address the reasons Latinos decide not to participate in preventive HIV vaccine trials.     

Sorting through search results: a content analysis of HPV vaccine information online

Introduction

Surveys have shown that many people now turn to the Internet for health information when making health-related decisions. This study systematically analyzed the HPV vaccine information returned by online search engines. HPV is the most common sexually transmitted disease and is the leading cause of cervical cancers.

Methods

We conducted a content analysis of 89 top search results from Google, Yahoo, Bing, and Ask.com. The websites were analyzed with respect to source, tone, information related to specific content analyzed through the lens of the Health Belief Model, and in terms of two content themes (i.e., conspiracy theories and civil liberties). The relations among these aspects of the websites were also explored.

Results

Most websites were published by nonprofit or academic sources (34.8%) and governmental agencies (27.4%) and were neutral in tone (57.3%), neither promoting nor opposing the HPV vaccine. Overall, the websites presented suboptimal or inaccurate information related to the five behavioral predictors stipulated in the Health Belief Model. Questions related to civil liberties were present on some websites.

Conclusion

Health professionals designing online communication with the intent of increasing HPV vaccine uptake should take care to include information about the risks of HPV, including susceptibility and severity. Additionally, websites should include information about the benefits of the vaccine (i.e., effective against HPV), low side effects as a barrier that can be overcome, and ways in which to receive the vaccine to raise individual self-efficacy.     

The cost-effectiveness of a modestly effective HIV vaccine in the United States

Background

The recent RV144 clinical trial showed that an ALVAC/AIDSVAX prime-boost HIV vaccine regimen may confer partial immunity in recipients and reduce transmission by 31%. Trial data suggest that efficacy may initially exceed 70% but decline over the following 3.5 years. Estimating the potential health benefits associated with a one-time vaccination campaign, as well as the projected benefits of repeat booster vaccination, may inform future HIV vaccine research and licensing decisions.

Methods

We developed a mathematical model to project the future course of the HIV epidemic in the United States under varying HIV vaccine scenarios. The model accounts for disease progression, infection transmission, antiretroviral therapy, and HIV-related morbidity and mortality. We projected HIV prevalence and incidence over time in multiple risk groups, and we estimated quality-adjusted life years (QALYs) and costs over a 10-year time horizon. We assumed an exponentially declining efficacy curve fit to trial data, and that subsequent vaccine boosters confer similar immunity. Variations in vaccine parameters were examined in sensitivity analysis.

Results

Under existing HIV prevention and treatment efforts, an estimated 590,000 HIV infections occur over 10 years. One-time vaccination achieving 60% coverage of adults could prevent 9.8% of projected new infections over 10 years (and prevent 34% of new infections in the first year) and cost approximately $91,000/QALY gained relative to the status quo, assuming $500 per vaccination series. Targeted vaccination strategies result in net cost savings for vaccines costing less than $750. One-time vaccination of 60% of all adults coupled with three-year boosters only for men who have sex with men and people who inject drugs could prevent 21% of infections for $81,000/QALY gained relative to vaccination of higher risk sub-populations only. A program attaining 90% vaccination coverage prevents 15% of new HIV cases over 10 years (and approximately 50% of infections in the first year).

Conclusions

A partially effective HIV vaccine with effectiveness similar to that observed in the RV144 trial would provide large health benefits in the United States and could meet conventionally accepted cost-effectiveness thresholds. Strategies that prioritize key populations are most efficient, but broader strategies provide greater total population health benefit.     

Perceived social support of HIV/AIDS orphans: a review

HIV/AIDS orphans are a vulnerable and disadvantaged group. The HIV/AIDS orphans’ crisis is an emerging problem of developing societies. Existing research, literature, and findings on perceived social support (PSS) of HIV/AIDS orphans in the world till date have been compiled with the aim of presenting the current status of research, major findings, and gaps in this area. A thorough review of published empirical studies from PubMed, PsycINFO databases, online publications of several organizations, web searches, and several online journals related to PSS of HIV/AIDS orphans have been reviewed. HIV/AIDS orphans from 6 to 18 years, whose either or both parents had died due to HIV/AIDS or were staying with HIV-positive parents were selected for this purpose. Six out of eight studies found low level of PSS in HIV/AIDS orphans and two studies found peer-group intervention very effective to improved PSS in HIV/AIDS orphans. They severely experience negative emotions, behavioral problems, higher levels of psychological difficulties, and poor academic performances due to the reasons like drawn out-of-school, living with an unaffectionate caretaker, inadequate care, child labor, physical and sexual abuse, stigma, and discrimination. The psychological health of HIV/AIDS orphans is at risk, and prevention and intervention efforts are missing for improving their psychological outcomes. The review recommends that a rigorous research needs to be prioritized so that the programs and policymakers that are attempting to work for their well-being may get helpful information to design evidence-based interventions.     

Socioecological influences on community involvement in HIV vaccine research

Objective

This study investigated socioecological factors influencing HIV vaccine research participation among communities living in geographic areas with high HIV prevalence and high poverty rates.

Methods

We surveyed a sample of 453 adults ≤18 years from areas of high poverty and high HIV prevalence in metro Atlanta and differentiated the effects of individual-, social/organizational-, and community-level characteristics on participation in HIV vaccine research via multilevel modeling techniques that incorporated questionnaire, program, and census data.

Results

Models that adjusted for both individual-level covariates (such as race, gender, attitudes, and beliefs concerning HIV research), social/organizational- and community-level factors such as local HIV prevalence rates, revealed that the extent of HIV prevention-related programs and services in census tracts contributed to individuals’ likelihood of participation in an HIV vaccine study. Additionally, neighborhood-based organizations offering HIV medical and treatment programs, support groups, and services (e.g., food, shelter, and clothing) encourage greater HIV vaccine research participation.

Conclusions

The findings support the hypothesis that community-level factors facilitate participation in HIV vaccine research independent of both individual- and social/organizational-level factors.     

Cognitive factors and willingness to participate in an HIV vaccine trial among HIV-negative injection drug users

This cross-sectional study involving a cohort of injection drug users (IDU) examined the relationship between cognitive factors (HIV treatment optimism, self-efficacy and knowledge of vaccine trial concepts) as well as risk factors for seroconversion, and willingness to participate (WTP) in a preventive phase 3 HIV vaccine trial. Willingness to participate overall was 56%. In a multivariate analysis, for a 20-unit increase in a 100-point composite scale, self-efficacy was positively related to WTP (adjusted odds ratio [AOR] = 1.95, 95% CI = 1.40–2.70). HIV treatment optimism and knowledge of vaccine trial concepts were unrelated to WTP. Aboriginal ethnicity (AOR = 3.47, 95% CI = 1.68–7.18) and a higher educational level (≥high school) (AOR = 1.96, 95% CI = 1.07–3.59) were positively related to WTP. This study provides information on WTP for an HIV vaccine trial. Limitations and future directions are also discussed.     

On the analysis of viral load endpoints in HIV vaccine trials

First generation HIV vaccines are not likely to provide complete protection from HIV-1 infection. Therefore, it is important to assess a vaccine's effect on disease progression and infectiousness of infected vaccinees in an efficacy trial; however, direct assessment of such vaccine effects is not feasible within current trial designs. Viral load in HIV-infected individuals correlates with infectiousness and disease progression in a natural history setting, and thus is a reasonable candidate for a surrogate outcome in vaccine efficacy trials. We consider comparisons of viral load of infected vaccinees to that of infected trial participants in the control group. Dramatic differences in viral loads between these groups would suggest a vaccine effect on disease progression. However, modest differences, even if statistically significant, could be consistent with an imperfect vaccine effect on susceptibility to infection and not an effect on disease progression, that is, a selection effect of the vaccine. Thus, the usual statistical tests for no difference between groups do not test the biologically and clinically relevant hypothesis. We propose a model for the possible selective effects of a vaccine and develop several test statistics for assessing a direct effect of the vaccine on viral load given this selection model. Finite sample properties of these tests are evaluated using computer simulations.     

Willingness to participate in HIV vaccine clinical trials among Chinese men who have sex with men

HIV vaccine trials require volunteers. Little is known about willingness to participate (WTP) in HIV vaccine trials among Chinese MSM. A survey of 550 MSM was conducted from March to June 2008, in Beijing, China. Data were collected on demographics, behaviors, perceptions about HIV/AIDS and HIV vaccines, and concerns about participation in HIV vaccine clinical trials. Of study participants, 35.8% were definitely willing to participate, 35.1% were probably willing, 16.4% were probably not willing, and 12.7% were definitely not willing. Analyses suggest that perceived family support, perceived protection against HIV infection and fear that participation would result in social distancing were associated with WTP. MSM in China may be good candidates for HIV vaccine trials. Further studies are needed to evaluate actual enrollment.     

The methodology of HIV/AIDS impact studies: a review of current practices

This review of studies on the socio-economic impact of HIV/AIDS shows that diversity in methodological design, which often is a result of practical considerations and resource constraints rather than of poor design, is the norm. This limits the comparability of research findings. More detailed reporting on method, which is not the norm, can go some way towards facilitating such comparison. Furthermore, the review underlines the importance of exploring intervention issues in more detail. Researchers need to employ results in answering specific policy questions. Scope remains for more impact studies to be conducted in developing countries in general and in certain high prevalence countries in specific, i.e. Southern Africa. Studies that explore the urban/rural dynamics of and clients' perceptions and behavior in seeking care and support are necessary to better understand the epidemic. The role of community-based organizations, non-governmental organizations and other stakeholders in studies of this nature can be expanded. Larger studies generally have more statistical power, but smaller, in-depth studies can be equally valuable. A careful stratification of sample populations can enhance the quality of cross-sectional studies. Qualitative methods should be used to complement the current reliance on survey-based methods of data collection. More longitudinal studies are required to explore the long-term impacts of HIV/AIDS. HIV/AIDS training for fieldworkers should be standard in studies of this nature, while cognizance should be taken of the dangers of employing local people as fieldworkers in studies of such sensitive nature. Scope remains for the further empirical analysis of data from impact studies, which requires these data sets being made accessible to more researchers. In the longer term, an attempt at standardizing core modules in impact studies can help to improve our understanding of the impact of HIV/AIDS in different settings.     

The potential impact of a moderately effective HIV vaccine with rapidly waning protection in South Africa and Thailand

Background

Although published data from the recent ALVAC/AIDSVAX trial in Thailand (RV144) indicated the HIV vaccine provided very modest protection overall (31.2%), new analysis of trial data has suggested higher efficacy levels earlier in the follow-up period. CDC and UNAIDS organized several modeling research teams to explore the implications of the trial results and potential utility of this vaccine.

Methods

We explored the impact of a vaccine with moderate but rapidly waning protection (78%, 1.43 years) using an exponential decay function fit to trial data. We varied program coverage levels (20-80%), vaccine efficacy (30-90%), timing (single or multi-year programs), targeting (general or populations at higher risk), and background levels of all other prevention programs (constant or scaled-up). We simulated these various vaccination scenarios in two representative countries using demographic projections generated with Spectrum modeling software. We assumed the vaccine becomes available in 2020 and target coverage is achieved by 2025.

Results

A general vaccination strategy in South Africa covering 60% of the population, for example, would prevent 3.0 million infections between 2020 and 2030—36% of expected infections—and would be very effective, requiring only 39 vaccinations/infection averted. The same strategy in Thailand would prevent 81,000 infections—35% of expected infections—but would require 1725 vaccinations/infection averted. Targeting only populations at higher risk of exposure in Thailand would reduce total vaccinations given by more than ten-fold and would still prevent 52,000 infections—23% of expected infections—while requiring only 220 vaccinations/infection averted. Outcomes were sensitive to program coverage, vaccine efficacy and background levels of all other prevention programs.

Conclusions

A vaccine with rapidly waning protection could have a substantial impact on the epidemic in South Africa and Thailand. Due to the short duration of effect, large numbers of vaccinations would be needed to maintain high population coverage levels. Further research into the immunological effects of booster vaccinations is warranted.     

Adolescent decision making about participation in a hypothetical HIV vaccine trial

PurposeThe purpose of this study was to examine the process of adolescent decision-making about participation in an HIV vaccine clinical trial, comparing it to adult models of informed consent with attention to developmental differences.MethodsAs part of a larger study of preventive misconception in adolescent HIV vaccine trials, we interviewed 33 male and female 16–19-year-olds who have sex with men. Participants underwent a simulated HIV vaccine trial consent process, and then completed a semistructured interview about their decision making process when deciding whether or not to enroll in and HIV vaccine trial. An ethnographic content analysis approach was utilized.ResultsTwelve concepts related to adolescents’ decision-making about participation in an HIV vaccine trial were identified and mapped onto Appelbaum and Grisso's four components of decision making capacity including understanding of vaccines and how they work, the purpose of the study, trial procedures, and perceived trial risks and benefits, an appreciation of their own situation, the discussion and weighing of risks and benefits, discussing the need to consult with others about participation, motivations for participation, and their choice to participate.ConclusionThe results of this study suggest that most adolescents at high risk for HIV demonstrate the key abilities needed to make meaningful decisions about HIV vaccine clinical trial participation.     

Expected epidemiological impact of the introduction of a partially effective HIV vaccine among men who have sex with men in Australia

A trial of the ALVAC-AIDSVAX HIV vaccine was recently found to be partially effective in preventing HIV transmission among study participants in Thailand. The success of this trial means that vaccination may become a viable intervention for the prevention of HIV infection in the medium-term future. Assuming that the vaccine has similar relative protective effectiveness per exposure event for reducing transmission among men who have sex with men (MSM) in high-income settings we investigated the potential population-level impact of rolling out such a vaccine among MSM in New South Wales, Australia. Using a detailed individual-based transmission model that simulates a population of sexually active MSM it was found that one-off intervention of 60% or 30% coverage of a vaccine with characteristics like the ALVAX-AIDSVAX vaccine would likely reduce the cumulative incidence of HIV by 9.6% and 5.1%, respectively, over a 10-year period. Due to the waning of vaccine efficacy, a booster vaccination could be required to maintain this reduction in incidence over the long term. If the previously vaccinated population is given a booster vaccine, with the same protection conferred as with the initial vaccination, every 5 years or every 2 years then the cumulative incidence over 10 years for 60% coverage could be reduced by 14.4% and 22.8%, respectively. Such a weak vaccine, with boosting, may be a potential intervention strategy for the prevention of HIV infection in MSM in high-income countries if further trials show boosting to be safe, acceptable, and cost-effective. However, the moderately low population-level impact suggests that a public health strategy involving such a vaccine should be supplemented with other biomedical and educational strategies.     

Assessing the feasibility of hepatitis C virus vaccine trials: Results from the Hepatitis C Incidence and Transmission Study-community (HITS-c) vaccine preparedness study

Efficacy trials of preventive hepatitis C virus (HCV) vaccine candidates raise challenging scientific and ethical issues. Based on data from the first 3 years of a community-based prospective observational study – the Hepatitis C Incidence and Transmission Study-community (HITS-c) – this paper examines the feasibility of conducting trials of candidate HCV vaccines with people who inject drugs (PWID) in Sydney, Australia. Of the 166 PWID confirmed HCV antibody negative and eligible for enrolment, 156 (94%) completed baseline procedures. Retention was high, with 89% of participants retained at 48 weeks and 76% of participants completing at least 75% of study visits within 2 weeks of schedule. The rate of primary HCV infection was 7.9/100 py (95% CI 4.9, 12.7). Of the 17 incident cases, 16 completed at least one follow-up assessment and 12 (75%) had evidence of chronic viraemia with progression to chronic HCV infection estimated to be 6/100 py. Power calculations suggest a chronic HCV infection rate of at least 12/100 py (primary HCV infection rate 16/100 py) will be required for stand-alone trials of highly efficacious candidates designed to prevent chronic infection. However, elevated primary HCV infection was observed among participants not receiving opioid substitution therapy who reported heroin as the main drug injected (26.9/100 py, 95% CI 14.5, 50.0) and those who reported unstable housing (23.5/100 py, 95% CI 7.6, 72.8), daily or more frequent injecting (22.7/100 py, 95% CI 12.2, 42.2) and receptive syringe sharing (23.6/100 py, 95% CI 9.8, 56.7) in the 6 months prior to baseline. These data suggest that it is possible to recruit and retain at-risk PWID who adhere to study protocols and that modification of eligibility criteria may identify populations with sufficiently high HCV incidence. Results support the feasibility of large multi-centre HCV vaccine trials, including in the Australian setting.     

Targeting and vaccine durability are key for population-level impact and cost-effectiveness of a pox-protein HIV vaccine regimen in South Africa

Background

RV144 is to date the only HIV vaccine trial to demonstrate efficacy, albeit rapidly waning over time. The HVTN 702 trial is currently evaluating in South Africa a similar vaccine formulation to that of RV144 for subtype C HIV with additional boosters (pox-protein regimen). Using a detailed stochastic individual-based network model of disease transmission calibrated to the HIV epidemic, we investigate population-level impact and maximum cost of an HIV vaccine to remain cost-effective.

The potential impact of an HIV vaccine with rapidly waning protection on the epidemic in Southern Africa: examining the RV144 trial results

Background

The prime-boost HIV vaccine regimen used in the recent RV144 trial resulted in modest efficacy of 31% over 3.5 years, but was substantially higher in the first year post-vaccination. We sought to explore the potential impact of a vaccine with rapidly waning efficacy in a South African population.

Methods

We explored two strategies using a dynamic compartmental epidemic model for heterosexual transmission of HIV: [1] vaccination of a single cohort (30%, 60% or 90% of the initial population), with exponentially waning efficacy, but booster vaccinations at 5- or 2-year intervals, and [2] continuous vaccination of the unvaccinated population at the same coverage levels (30%, 60% or 90%) but with a constant efficacy vaccine of short duration. We also examined potential changes in post-vaccination condom use.

Results

The single cohort vaccination strategies did not have a substantial impact on HIV prevalence, although without boosters they still prevented 2-6% of the expected infections at 20 years, depending on the population coverage. The 5-year and 2-year booster strategies prevented 8-24% and 17-45% of the expected infections, respectively. Continuous vaccination to maintain population coverage levels resulted in more substantial reductions in population HIV prevalence and greater numbers of infections prevented: HIV prevalence at 20 years was reduced from 23% to 8-14% and the number of expected infections was decreased by 34-59%, depending on the population coverage level. Moderate changes in post-vaccination condom use did not substantially affect these outcomes.

Conclusions

An HIV vaccine with partial efficacy and declining protection similar to the RV144 vaccine could prevent a substantial proportion of HIV infections if booster vaccinations were effective and available. Our estimates of the population impact of vaccination would be improved by further understanding of the duration of protection, the effectiveness of booster vaccination, and whether the vaccine efficacy varies between subpopulations at higher and lower risk of exposure.