Potential future impact of a partially effective HIV vaccine in a southern African setting

HIV infection

The AIDS epidemic has been a global public health issue for more than 40 years and has resulted in ~40 million deaths. AIDS is caused by the retrovirus, HIV-1, which is transmitted via body fluids and secretions. After infection, the virus invades host cells by attaching to CD4 receptors and thereafter one of two major chemokine coreceptors, CCR5 or CXCR4, destroying the host cell, most often a T lymphocyte, as it replicates. If unchecked this can lead to an immune-deficient state and demise over a period of ~2-10 years. The discovery and global roll-out of rapid diagnostics and effective antiretroviral therapy led to a large reduction in mortality and morbidity and to an expanding group of individuals requiring lifelong viral suppressive therapy. Viral suppression eliminates sexual transmission of the virus and greatly improves health outcomes. HIV infection, although still stigmatized, is now a chronic and manageable condition. Ultimate epidemic control will require prevention and treatment to be made available, affordable and accessible for all. Furthermore, the focus should be heavily oriented towards long-term well-being, care for multimorbidity and good quality of life. Intense research efforts continue for therapeutic and/or preventive vaccines, novel immunotherapies and a cure.

Evaluation of novel HIV vaccine candidates using recombinant vesicular stomatitis virus vector produced in serum-free Vero cell cultures

Acquired Immune Deficiency Syndrome (AIDS) in humans is a result of the destruction of the immune system caused by Human Immunodeficiency Virus (HIV) infection. This serious epidemic is still progressing world-wide. Despite advances in treatment, a safe and effective preventive HIV vaccine is desired to combat this disease, and to save millions of lives. However, such a vaccine is not available yet although extensive amounts of resources in research and development have been invested over three decades. In light of the recently approved Ebola virus disease vaccine based on a recombinant vesicular stomatitis virus (rVSV-ZEBOV), we present the results of our work on three novel VSV-vectored HIV vaccine candidates. We describe the design, rescue, production and purification method and evaluate their immunogenicity in mice prior to preclinical studies that will be performed in non-human primates. The production of each of the three candidate vaccines (rVSV-B6-NL4.3Env/SIVtm, rVSV-B6-NL4.3Env/Ebtm and rVSV-B6-A74Env(PN6)/SIVtm) was evaluated in small scale in Vero cells and it was found that production kinetics on Vero cells vary depending on the HIV gp surface protein used. Purified virus preparations complied with the WHO restrictions for the residual DNA and host cell protein contents. Finally, when administered to mice, all three rVSV-HIV vaccine candidates induced an HIV gp140-specific antibody response.

Strengthening the scale-up and uptake of effective interventions for sex workers for population impact in Zimbabwe

Introduction

UNAIDS’ goal of ending AIDS by 2030 is unreachable without better targeting of testing, prevention and care. Female sex workers (FSW) in Zimbabwe are at high risk of HIV acquisition and transmission. Here, we report on collated programme and research data from Zimbabwe's national sex work programme. We also assess the potential for wider population impact of FSW programmes by modelling the impact on HIV incidence of eliminating transmission through FSW (i.e. calculate the population attributable fraction of incidence attributable to sex work).

Methods

Descriptive analyses of individual‐level programme data collected from FSW between 2009 and June 2018 are triangulated with data collected through 37 respondent driven sampling surveys from 19 sites in Zimbabwe 2011 to 2017. We describe programme coverage, uptake, retention and patterns of sex work behaviour and gaps in service provision. An individual‐level stochastic simulation model is used to reconstruct the epidemic and then the incidence compared with the counter‐factual trend in incidence from 2010 had transmission through sex work been eliminated from that date.

Results

Sisters has reached >67,000 FSW since 2009, increasing attendance as number of sites, programme staff and peer educators were increased. Over 57% of all FSW estimated to be working in Zimbabwe in 2017 (n = 40,000) attended the programme at least once. The proportion of young FSW reached has increased with introduction of the “Young Sisters programme.” There are no clear differences in pattern of sex work across settings. Almost all women report condom use with clients at last sex (95%); however, consistent condom use with clients in the last month varies from 52% to 95% by site. Knowledge of HIV‐positive status has increased from 48 to 78% between 2011 and 2016, as has prevalence of ART use among diagnosed women (29 to 67%). Although subject to uncertainty, modelling suggests that 70% (90% range: 32%, 93%) of all new infections in Zimbabwe from 2010 are directly or indirectly attributable to transmission via sex work.

Conclusions

It is feasible to increase coverage and impact of sex work programming through community‐led scale‐up of evidence‐based interventions. Eliminating transmission through commercial sex would likely have a substantial impact on new infections occurring more widely across Zimbabwe.

The future of a partially effective HIV vaccine: assessing limitations at the population level

OBJECTIVES

Mathematical models have unanimously predicted that a first-generation HIV vaccine would be useful and cost-effective to roll out, but that its overall impact would be insufficient to reverse the epidemic. Here, we explore what factors contribute most to limiting the impact of such a vaccine.

METHODS

Ranging from a theoretical ideal to a more realistic regimen, mirroring the one used in the currently ongoing trial in South Africa (HVTN 702), we model a nested hierarchy of vaccine attributes such as speed of scale-up, efficacy, durability, and return rates for booster doses.

RESULTS

The predominant reasons leading to a substantial loss of vaccine impact on the HIV epidemic are the time required to scale up mass vaccination, limited durability, and waning of efficacy.

CONCLUSIONS

A first-generation partially effective vaccine would primarily serve as an intermediate milestone, furnishing correlates of immunity and platforms that could serve to accelerate future development of a highly effective, durable, and scalable next-generation vaccine capable of reversing the HIV epidemic.

Taking stock of the present and looking ahead: envisioning challenges in the design of future HIV prevention efficacy trials

Despite the recent success of antiretrovirals for HIV prevention, additional, more effective, or more acceptable biomedical interventions will ultimately be needed to end the HIV epidemic. Designing clinical trials to evaluate the efficacy of new products that reduce HIV infection risk is challenging because of the existence of highly effective interventions to prevent HIV. However, the implementation of these interventions is uneven, and the fact that multiple HIV prevention efficacy trials are currently evaluating new products means the field confronts uncertainty in the emerging standard of prevention. In this Viewpoint, we take stock of the current state of HIV prevention, and subsequently discuss the key challenges in designing future trials to evaluate the next generation of HIV prevention products. We also highlight gaps in the knowledge base that need to be addressed to advance the design of research. Future trials are tenable, even in the context of existing and effective interventions, and should involve careful statistical approaches and multidisciplinary collaborative design.

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.

METHODS

Consistent with the original pox-protein regimen, we model a primary series of five vaccinations meeting the goal of 50% cumulative efficacy 24 months after the first dose and include two-yearly boosters that maintain durable efficacy over 10 years. We simulate vaccination programs in South Africa starting in 2027 under various vaccine targeting and HIV treatment and prevention assumptions.

RESULTS

Our analysis shows that this partially effective vaccine could prevent, at catch-up vaccination with 60% coverage, up to 941,000 (15.6%) new infections between 2027 and 2047 assuming current trends of antiretroviral treatment. An impact of up to 697,000 (11.5%) infections prevented could be achieved by targeting age cohorts of highest incidence. Economic evaluation indicates that, if treatment scale-up was achieved, vaccination could be cost-effective at a total cost of less than $385 and $62 per 10-year series (cost-effectiveness thresholds of $5,691 and $750).

CONCLUSIONS

While a partially effective, rapidly waning vaccine could help to prevent HIV infections, it will not eliminate HIV as a public health priority in sub-Saharan Africa. Vaccination is expected to be most effective under targeted delivery to age groups of highest HIV incidence. Awaiting results of trial, the introduction of vaccination should go in parallel with continued innovation in HIV prevention, including studies to determine the costs of delivery and feasibility and further research into products with greater efficacy and durability.

'Why would you promote something that is less percent safer than a condom?': Perspectives on partially effective HIV prevention technologies among key populations in South Africa

New biomedical prevention technologies (NPTs) for HIV, including oral Pre-Exposure Prophylaxis, and vaginal and rectal microbicides and HIV vaccines in development, may contribute substantially to controlling the HIV epidemic. However, their effectiveness is contingent on product acceptability and adherence. We explored perceptions and understanding of partially effective NPTs with key populations in South African townships. From October 2013 to February 2014, we conducted six focus groups and 18 individual interviews with Xhosa-speaking adolescents (n = 14), adult men who have sex with men (MSM) (n = 15), and adult heterosexual men (n = 9) and women (n = 10), and eight key informant (KI) interviews with healthcare workers. Interviews/focus groups were transcribed and reviewed using a thematic approach and framework analysis. Overall, participants and KIs indicated scepticism about NPTs that were not 100% efficacious. Some participants equated not being 100% effective with not being completely safe, and thus not appropriate for dissemination. KIs expressed concerns that promoting partially effective NPTs would encourage substitution of a more effective with a less effective method or encourage risk compensation. Educational and social marketing interventions that address the benefits and appropriate use of partially effective NPTs, including education and support tailored for frontline service providers, are needed to prepare for successful NPT implementation in South Africa.

HIV, HCV and HBV: A Review of Parallels and Differences

Elimination of the three blood-borne viruses—human immunodeficiency virus (HIV), hepatitis B (HBV) and hepatitis C (HCV)—as public health issues may be plausible in the near future. Spectacular advances have been made with the introduction of highly effective antiviral agents into clinical practice, and prevention strategies are available for all three infections. Effective disease control, laid out by WHO global strategies, is currently feasible for all three viruses. However, for worldwide elimination of these viruses, effective vaccines are required that are currently only available for HBV. In this review differences and parallels among HIV, HCV and HBV will be discussed with a focus on virologic and therapeutic issues, and prospects for the future of HBV will be presented.

HIV population-level adaptation can rapidly diminish the impact of a partially effective vaccine

BACKGROUND

Development of an HIV vaccine might be essential to ending the HIV/AIDS pandemic. However, vaccines can result in the emergence and spread of vaccine-resistant strains. Indeed, analyses of breakthrough infections in the HIV phase 3 vaccine trial RV144 identified HIV genotypes with differential rates of transmission in vaccine and placebo recipients. We hypothesized that, for HIV vaccination programs based on partially effective vaccines similar to RV144, HIV adaptation will rapidly diminish the expected vaccine impact.

METHODS AND FINDINGS

Using two HIV epidemic models, we simulated large-scale vaccination programs and, critically, included HIV strain diversity with respect to the vaccine response. We show here that rapid population-level viral adaptation can lead to decreased overall vaccine efficacy and substantially fewer infections averted by vaccination, when comparing scenarios with and without viral evolution (with outcomes depending on vaccination coverage, vaccine efficacy against the sensitive allele, and the initial resistant allele frequency). Translating this to the epidemic in South Africa, a scenario with 70% vaccination coverage may result in 250,000 infections (non-averted by vaccination) within 10 years of vaccine rollout that are due solely to HIV adaptation, all else being equal.

CONCLUSIONS

These findings suggest that approaches to HIV vaccine development, program implementation, and epidemic modeling may require attention to viral adaptation in response to vaccination.

Hope for HIV control in southern Africa: The continued quest for a vaccine

In a Perspective, Linda-Gail Bekker and Glenda Gray discuss HIV vaccine development.

Identifying Key Drivers of the Impact of an HIV Cure Intervention in Sub-Saharan Africa

BACKGROUND

It is unknown what properties would be required to make an intervention in low income countries that can eradicate or control human immunodeficiency virus (HIV) without antiretroviral therapy (ART) cost-effective.

METHODS

We used a model of HIV and ART to investigate the effect of introducing an ART-free viral suppression intervention in 2022 using Zimbabwe as an example country. We assumed that the intervention (cost: $500) would be accessible for 90% of the population, be given to those receiving effective ART, have sufficient efficacy to allow ART interruption in 95%, with a rate of viral rebound of 5% per year in the first 3 months, and a 50% decline in rate with each successive year.

RESULTS

An ART-free viral suppression intervention with these properties would result in >0.53 million disability-adjusted-life-years averted over 2022-2042, with a reduction in HIV program costs of $300 million (8.7% saving). An intervention of this efficacy costing anything up to $1400 is likely to be cost-effective in this setting.

CONCLUSIONS

Interventions aimed at curing HIV infection have the potential to improve overall disease burden and to reduce costs. Given the effectiveness and cost of ART, such interventions would have to be inexpensive and highly effective.

Which New Health Technologies Do We Need to Achieve an End to HIV/AIDS?

In the last 15 years, antiretroviral therapy (ART) has been the most globally impactful life-saving development of medical research. Antiretrovirals (ARVs) are used with great success for both the treatment and prevention of HIV infection. Despite these remarkable advances, this epidemic grows relentlessly worldwide. Over 2.1 million new infections occur each year, two-thirds in women and 240,000 in children. The widespread elimination of HIV will require the development of new, more potent prevention tools. Such efforts are imperative on a global scale. However, it must also be recognised that true containment of the epidemic requires the development and widespread implementation of a scientific advancement that has eluded us to date--a highly effective vaccine. Striving for such medical advances is what is required to achieve the end of AIDS.

The Case for Adolescent HIV Vaccination in South Africa: A Cost-Effectiveness Analysis

Despite comprising 0.7% of the world population, South Africa is home to 18% of the global human immunodeficiency virus (HIV) prevalence. Unyielding HIV subepidemics among adolescents threaten national attempts to curtail the disease burden. Should an HIV vaccine become available, establishing its point of entry into the health system becomes a priority. This study assesses the impact of school-based HIV vaccination and explores how variations in vaccine characteristics affect cost-effectiveness. The cost per quality adjusted life year (QALY) gained associated with school-based adolescent HIV vaccination services was assessed using Markov modeling that simulated annual cycles based on national costing data. The estimation was based on a life expectancy of 70 years and employs the health care provider perspective. The simultaneous implementation of HIV vaccination services with current HIV management programs would be cost-effective, even at relatively higher vaccine cost. At base vaccine cost of US$ 12, the incremental cost effectiveness ratio (ICER) was US$ 43 per QALY gained, with improved ICER values yielded at lower vaccine costs. The ICER was sensitive to duration of vaccine mediated protection and variations in vaccine efficacy. Data from this work demonstrate that vaccines offering longer duration of protection and at lower cost would result in improved ICER values. School-based HIV vaccine services of adolescents, in addition to current HIV prevention and treatment health services delivered, would be cost-effective.

Dispelling myths and focusing on notable concepts in HIV pathogenesis

Since the discovery of HIV over three decades ago, major efforts have been made to control and perhaps eliminate HIV infection worldwide. During these studies, certain myths or misconceptions about this infectious disease have been emphasized and other potentially beneficial concepts have received less attention. A true long-term solution to HIV infection merits an appreciation of alternative ideas and findings that could be beneficial in the ultimate control of HIV/AIDS. Here, I discuss six issues and call for more attention to the science of HIV and well-designed clinical trials.