The last decade of microbicide clinical trials in Africa: from hypothesis to facts

A unique class of lignin derivatives displays broad anti-HIV activity by interacting with the viral envelope

In Gordts et al. (2015), we have shown that lignosulfonic acid, a commercially available lignin derivative, possesses broad antiviral activity against human immunodeficiency virus (HIV) and Herpes simplex virus (HSV) by preventing viral entry into susceptible target cells. Because of the interesting safety profile as potential microbicide, we now determined the antiviral activity of a series of lignosulfonates in order to understand better which molecular features can contribute to their antiviral activity. Here, 24 structurally different lignosulfonates were evaluated for their capacity to inhibit HIV and HSV transmission and replication in various cellular assays. These derivatives differ in origin (hardwood or softwood), counter-ion used during sulphite processing (Na⁺, Ca²⁺, or NH₄⁺), sulphur content, carboxylic acid percentage, and molecular weight fraction, which allowed to determine structure-activity relationships. We demonstrate that the broad antiviral activity of lignosulfonates is mainly dependent on their molecular weight and that their mechanism of action is based on interactions with the viral envelope glycoproteins. This makes the lignosulfonates a potential low-cost microbicide that protects women from sexual HIV and HSV transmission and thus prevents life-long infection.

Nanomedicine in the development of anti-HIV microbicides

Prevention plays an invaluable role in the fight against HIV/AIDS. The use of microbicides is considered an interesting potential approach for topical pre-exposure prophylaxis of HIV sexual transmission. The prospects of having an effective product available are expected to be fulfilled in the near future as driven by recent and forthcoming results of clinical trials. Different dosage forms and delivery strategies have been proposed and tested for multiple microbicide drug candidates presently at different stages of the development pipeline. One particularly interesting approach comprises the application of nanomedicine principles to the development of novel anti-HIV microbicides, but its implications to efficacy and safety are not yet fully understood. Nanotechnology-based systems, either presenting inherent anti-HIV activity or acting as drug nanocarriers, may significantly influence features such as drug solubility, stability of active payloads, drug release, interactions between active moieties and virus/cells, intracellular drug delivery, drug targeting, safety, antiviral activity, mucoadhesive behavior, drug distribution and tissue penetration, and pharmacokinetics. The present manuscript provides a comprehensive and holistic overview of these topics as relevant to the development of vaginal and rectal microbicides. In particular, recent advances pertaining inherently active microbicide nanosystems and microbicide drug nanocarriers are discussed.

Repeated Vaccination of Cows with HIV Env gp140 during Subsequent Pregnancies Elicits and Sustains an Enduring Strong Env-Binding and Neutralising Antibody Response

An important feature of a potential vaccine against HIV is the production of broadly neutralising antibodies (BrNAbs) capable of potentially blocking infectivity of a diverse array of HIV strains. BrNAbs naturally arise in some HIV infected individuals after several years of infection and their serum IgG can neutralise various HIV strains across different subtypes. We previously showed that vaccination of cows with HIV gp140 AD8 trimers resulted in a high titre of serum IgG against HIV envelope (Env) that had strong BrNAb activity. These polyclonal BrNAbs concentrated into the colostrum during the late stage of pregnancy and can be harvested in vast quantities immediately after calving. In this study, we investigated the effect of prolonged HIV gp140 vaccination on bovine colostrum IgG HIV Env-binding and BrNAb activity over subsequent pregnancies. Repeated immunisation led to a maintained high titre of HIV Env specific IgG in the colostrum batches, but this did not increase through repeated cycles. Colostrum IgG from all batches also strongly competed with sCD4 binding to gp140 Env trimer and with human-derived monoclonal VRC01 and b12 BrNAbs that bind the CD4 binding site (CD4bs). Furthermore, competition neutralisation assays using RSC3 Env gp120 protein core and a derivative CD4bs mutant, RSC3 Δ371I/P363N, showed that CD4bs neutralising antibodies contribute to the neutralising activity of all batches of purified bovine colostrum IgG. This result indicates that the high IgG titre/avidity of anti-CD4bs antibodies with BrNAb activity was achieved during the first year of vaccination and was sustained throughout the years of repeated vaccinations in the cow tested. Although IgG of subsequent colostrum batches may have a higher avidity towards the CD4bs, the overall breadth in neutralisation was not enhanced. This implies that the boosting vaccinations over 4 years elicited a polyclonal antibody response that maintained the proportion of both neutralising and non-neutralising CD4bs antibodies.

The Art of HIV Elimination: Past and Present Science

INTRODUCTION

Remarkable strides have been made in controlling the HIV epidemic, although not enough to achieve epidemic control. More recently, interest in biomedical HIV control approaches has increased, but substantial challenges with the HIV cascade of care hinder successful implementation. We summarise all available HIV prevention methods and make recommendations on how to address current challenges.

DISCUSSION

In the early days of the epidemic, behavioural approaches to control the HIV dominated, and the few available evidence-based interventions demonstrated to reduce HIV transmission were applied independently from one another. More recently, it has become clear that combination prevention strategies targeted to high transmission geographies and people at most risk of infections are required to achieve epidemic control. Biomedical strategies such as male medical circumcision and antiretroviral therapy for treatment in HIV-positive individuals and as pre-exposure prophylaxis in HIV-negative individuals provide immense promise for the future of HIV control. In resource-rich settings, the threat of HIV treatment optimism resulting in increased sexual risk taking has been observed and there are concerns that as ART roll-out matures in resource-poor settings and the benefits of ART become clearly visible, behavioural disinhibition may also become a challenge in those settings. Unfortunately, an efficacious vaccine, a strategy which could potentially halt the HIV epidemic, remains elusive.

CONCLUSION

Combination HIV prevention offers a logical approach to HIV control, although what and how the available options should be combined is contextual. Therefore, knowledge of the local or national drivers of HIV infection is paramount. Problems with the HIV care continuum remain of concern, hindering progress towards the UNAIDS target of 90-90-90 by 2020. Research is needed on combination interventions that address all the steps of the cascade as the steps are not independent of each other. Until these issues are addressed, HIV elimination may remain an unattainable goal.

Recent advances on anti-HIV vaginal delivery systems development

A review of the recent outcomes regarding technologies to prevent vaginal transmission of HIV, mainly by using antiretroviral (ARV) drugs formulated as microbicides. An introduction about the HIV transmission mechanisms by the vaginal route is included, together with the recent challenges faced for development of successful microbicide products. The outcomes of clinical evaluations are mentioned, and the different formulation strategies studied to-date, with the requirements, advantages, disadvantages and limitations of each dosage-form type, are presented. Finally, the recent attempts to apply various types of nanotechnologies in order to develop advanced microbicide-products and overcome existing limitations, are discussed.

The Interaction between Human Immunodeficiency Virus and Human Papillomaviruses in Heterosexuals in Africa

Sub-Saharan Africa has the highest incidence of human papillomavirus (HPV) and cervical cancer in the world, which is further aggravated by the burden of human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS) disease with invasive cervical cancer being an AIDS-defining cancer. The prevalence of HPV infection and associated disease is very high in HIV-infected people and continues to be a problem even after anti-retroviral therapy. In the genital tract, the interaction between HPV and HIV is complex, with infection with multiple HPV types reported to make both women and men more susceptible to HIV infection. Besides the national programmes to vaccinate girls against HPV and screen women for cervical cancer, there should be targeted cervical cancer screening, treatment and prevention programmes introduced into HIV treatment centres. There is evidence that in high HIV prevalence areas, HIV-positive women could cause increases in the prevalence of genital HPV infection in HIV-negative men and so increase the HPV circulating in the community. Condom use and circumcision reduce the acquisition of HIV-1, and also to some extent of HPV. This review will highlight what is known about the interaction of HIV and HPV, with an emphasis on research in Africa.

Protein and oligonucleotide delivery systems for vaginal microbicides against viral STIs

Intravaginal delivery offers an effective option for localized, targeted, and potent microbicide delivery. However, an understanding of the physiological factors that impact intravaginal delivery must be considered to develop the next generation of microbicides. In this review, a comprehensive discussion of the opportunities and challenges of intravaginal delivery are highlighted, in the context of the intravaginal environment and currently utilized dosage forms. After a subsequent discussion of the stages of microbicide development, the intravaginal delivery of proteins and oligonucleotides is addressed, with specific application to HSV and HIV. Future directions may include the integration of more targeted delivery modalities to virus and host cells, in addition to the use of biological agents to affect specific genes and proteins involved in infection. More versatile and multipurpose solutions are envisioned that integrate new biologicals and materials into potentially synergistic combinations to achieve these goals.

Factores solubles con actividad antiviral: en búsqueda de nuevos blancos terapéuticos para la infección por el VIH-1

Los mecanismos innatos antivirales han resultado de gran interés debido a su uso potencial para la prevención y tratamiento de la infección por el VIH. En particular, los factores solubles antivirales han sido objeto de múltiples investigaciones por su capacidad de inhibir diferentes pasos del ciclo replicativo viral y de potenciar la respuesta inmune del hospedero. Entre estos factores solubles se destacan TRIM-5α, APOBEC3G, SAMHD1, ELAFIN, SERPINA1 y SLPI, que actúan directamente sobre la partícula viral o la célula, o promueven la producción de moléculas involucradas en la respuesta inmune contra el virus. Algunos de ellos se han correlacionado con un bajo riesgo de adquirir la infección por el VIH o con una lenta progresión a sida. La exploración de los mecanismos antivirales de estas proteínas es requisito para el desarrollo de nuevas alternativas terapéuticas.

Poly(ethylene glycol) (PEG)-lactic acid nanocarrier-based degradable hydrogels for restoring the vaginal microenvironment

Women with bacterial vaginosis (BV) display reduced vaginal acidity, which make them susceptible to associated infections such as HIV. In the current study, poly(ethylene glycol) (PEG) nanocarrier-based degradable hydrogels were developed for the controlled release of lactic acid in the vagina of BV-infected women. PEG-lactic acid (PEG-LA) nanocarriers were prepared by covalently attaching lactic acid to 8-arm PEG-SH via cleavable thioester bonds. PEG-LA nanocarriers with 4 copies of lactic acid per molecule provided controlled release of lactic acid with a maximum release of 23% and 47% bound lactic acid in phosphate buffered saline (PBS, pH7.4) and acetate buffer (AB, pH4.3), respectively. The PEG nanocarrier-based hydrogels were formed by cross-linking the PEG-LA nanocarriers with 4-arm PEG-NHS via degradable thioester bonds. The nanocarrier-based hydrogels formed within 20 min under ambient conditions and exhibited an elastic modulus that was 100-fold higher than the viscous modulus. The nanocarrier-based degradable hydrogels provided controlled release of lactic acid for several hours; however, a maximum release of only 10%-14% bound lactic acid was observed possibly due to steric hindrance of the polymer chains in the cross-linked hydrogel. In contrast, hydrogels with passively entrapped lactic acid showed burst release with complete release within 30 min. Lactic acid showed antimicrobial activity against the primary BV pathogen Gardnerella vaginalis with a minimum inhibitory concentration (MIC) of 3.6 mg/ml. In addition, the hydrogels with passively entrapped lactic acid showed retained antimicrobial activity with complete inhibition G. vaginalis growth within 48 h. The results of the current study collectively demonstrate the potential of PEG nanocarrier-based hydrogels for vaginal administration of lactic acid for preventing and treating BV.

Nanoparticle-based drug delivery to the vagina: a review

Vaginal drug administration can improve prophylaxis and treatment of many conditions affecting the female reproductive tract, including sexually transmitted diseases, fungal and bacterial infections, and cancer. However, achieving sustained local drug concentrations in the vagina can be challenging, due to the high permeability of the vaginal epithelium and expulsion of conventional soluble drug dosage forms. Nanoparticle-based drug delivery platforms have received considerable attention for vaginal drug delivery, as nanoparticles can provide sustained release, cellular targeting, and even intrinsic antimicrobial or adjuvant properties that can improve the potency and/or efficacy of prophylactic and therapeutic modalities. Here, we review the use of polymeric nanoparticles, liposomes, dendrimers, and inorganic nanoparticles for vaginal drug delivery. Although most of the work toward nanoparticle-based drug delivery in the vagina has been focused on HIV prevention, strategies for treatment and prevention of other sexually transmitted infections, treatment for reproductive tract cancer, and treatment of fungal and bacterial infections are also highlighted.

Microbicides: topical prevention against HIV

Microbicides represent a potential intervention strategy for preventing HIV transmission. Vaginal microbicides would meet the need for a discreet method that women could use to protect themselves against HIV. Although early-generation microbicides failed to demonstrate efficacy, newer candidates are based on more potent antiretroviral (ARV) products. Positive data from the CAPRISA 004 trial of tenofovir gel support use in women and represent a turning point for the field. This article reviews current progress in development of ARV-based microbicides. We discuss the consensus on selection criteria, the potential for drug resistance, rationale for drug combinations, and the use of pharmacokinetic (PK)/pharmacodynamic (PD) assessment in product development. The urgent need for continued progress in development of formulations for sustained delivery is emphasized. Finally, as the boundaries between different prevention technologies become increasingly blurred, consideration is given to the potential synergy of diverse approaches across the prevention landscape.

A review of nanotechnological approaches for the prophylaxis of HIV/AIDS

Successful treatment and control of HIV/AIDS is one of the biggest challenges of 21st century. More than 33 million individuals are infected with HIV worldwide and more than 2 million new cases of HIV infection have been reported. The situation demands development of effective prevention strategies to control the pandemic of AIDS. Due to lack of availability of an effective HIV vaccine, antiretroviral drugs and nucleic acid therapeutics like siRNA have been explored for HIV prophylaxis. Clinical trials shave shown that antiretroviral drugs, tenofovir and emtricitabine can offer some degree of HIV prevention. However, complete prevention of HIV infection has not been achieved yet. Nanotechnology has brought a paradigm shift in the diagnosis, treatment and prevention of many diseases. The current review discusses potential of various nanocarriers such as dendrimers, polymeric nanoparticles, liposomes, lipid nanocarriers, drug nanocrystals, inorganic nanocarriers and nanofibers in improving efficacy of various modalities available for HIV prophylaxis.

Mucus-penetrating nanoparticles for vaginal drug delivery protect against herpes simplex virus

Incomplete coverage and short duration of action limit the effectiveness of vaginally administered drugs, including microbicides, for preventing sexually transmitted infections. We investigated vaginal distribution, retention, and safety of nanoparticles with surfaces modified to enhance transport through mucus. We show that mucus-penetrating particles (MPPs) provide uniform distribution over the vaginal epithelium, whereas conventional nanoparticles (CPs) that are mucoadhesive are aggregated by mouse vaginal mucus, leading to poor distribution. Moreover, when delivered hypotonically, MPPs were transported advectively (versus diffusively) through mucus deep into vaginal folds (rugae) within minutes. By penetrating into the deepest mucus layers, more MPPs were retained in the vaginal tract after 6 hours compared to CPs. After 24 hours, when delivered in a conventional vaginal gel, patches of a model drug remained on the vaginal epithelium, whereas the epithelium was coated with drug delivered by MPPs. We then developed MPPs composed of acyclovir monophosphate (ACVp). When administered before vaginal herpes simplex virus 2 challenge, ACVp-MPPs protected 53% of mice compared to only 16% protected by soluble drug. Overall, MPPs improved vaginal drug distribution and retention, provided more effective protection against vaginal viral challenge than soluble drug, and were nontoxic when administered daily for 1 week.

Virological and molecular characterization of a simian human immunodeficiency virus (SHIV) encoding the envelope and reverse transcriptase genes from HIV-1

Simian-human immunodeficiency virus encoding both reverse transcriptase (RT) and envelope genes of HIV-1 (RT Env SHIV) is important for evaluating biomedical prevention modalities for HIV/AIDS. We describe virological characterization of a clade B RT Env SHIV following infection of macaques via multiple routes. In vivo passage of the RT Env SHIV through Indian rhesus macaque enhanced infectivity. Expanded virus had minimal envelope heterogeneity and was inhibited by NNRTIs and CCR5 antagonists. Infection of macaques with RT Env SHIV via mucosal or intravenous routes resulted in stable infection accompanied by peak plasma viremia of approximately 5×10(6) copies/ml that was controlled beyond set point. Molecular homogeneity of the virus was maintained following in vivo passage. Inhibition of RT Env SHIV by RT and entry inhibitors and ease of in vivo transmission make it a useful model for testing the efficacy of combinations of entry and RT inhibitors in nonhuman primates.

The use of preexposure treatments for HIV prophylaxis

Infection with human immunodeficiency virus remains a global concern with a significant number of incident infections still reported worldwide. The use of prophylaxis prior to exposure to the virus to prevent infection has been a growing area of recent research. Results in nonhuman primates and clinical trials in high-risk patient populations using preexposure prophylaxis have shown promising results in terms of efficacy and safety, especially relating to oral preexposure prophylaxis. The potential use of oral antiretroviral agents traditionally used for human immunodeficiency virus treatment as prophylaxis raises interesting considerations, such as the best agents available for such a role, long-term safety in healthy individuals, and the potential development of resistance to these agents should infection occur. From a public health perspective, the cost-effectiveness of implementing this preventive strategy has not been fully defined at this point in time.

Microbicides for HIV prevention

Although the HIV incidence rate has slowed in some countries, HIV remains a serious health challenge, particularly in the developing world. The epidemic is increasingly feminised, with young women at high risk of acquiring the virus. There is thus a clear requirement for acceptable woman-initiated methods of HIV prevention. Foremost among these are vaginally-applied substances known as microbicides; early research into potential microbicides focussed on non-HIV-specific compounds such as surfactants and polyanionic entry inhibitors. However, proof of the microbicide concept as a viable prevention strategy was not provided until the CAPRISA 004 trial of a microbicide containing the HIV-specific antiretroviral tenofovir was completed in mid-2010. Confirmation of the proof of concept provided by CAPRISA 004 by at least two major trials will hopefully lead to licensure of the product by 2018. Parallel studies are planned to ascertain the feasibility of implementation of these products in the public sector with subsequent research focussed on appropriate and acceptable methods of delivery of the active ingredient, and to increase adherence through other delivery systems such as vaginal rings.

Cervicovaginal safety of the formulated, biguanide-based human immunodeficiency virus type 1 (HIV-1) inhibitor NB325 in a murine model

Vaginal microbicides that reduce or eliminate the risk of HIV-1 sexual transmission must do so safely without adversely affecting the integrity of the cervicovaginal epithelium. The present studies were performed to assess the safety of the biguanide-based antiviral compound NB325 in a formulation suitable for topical application. Experiments were performed using a mouse model of cervicovaginal microbicide application, which was previously shown to be predictive of topical agent toxicity revealed in microbicide clinical trials. Mice were exposed vaginally to unformulated NB325 or NB325 formulated in the hydroxyethyl cellulose “universal placebo.” Following exposures to formulated 1% NB325 for 10 min to 24 h, the vaginal and cervical epithelia were generally intact, although some areas of minimal vaginal epithelial damage were noted. Although formulated NB325 appeared generally safe for application in these studies, the low but observable level of toxicity suggests the need for improvements in the compound and/or formulation.

Antiretroviral-based microbicides and oral pre-exposure prophylaxis for HIV prevention

Numerous HIV prevention options have been tested, with limited success. Microbicides have been the focus of research specifically targeted to prevent new infections among women. After decades of research using non-HIV-specific microbicides, we now have proof of concept for antiretroviral-based microbicides. Issues of drug resistance, frequency of HIV testing and adherence to treatment remain to be explored. Drugs used for HIV treatment and with good safety profiles have been shown to provide protection to men who have sex with men. Ethical issues surrounding cost, access, future design of HIV prevention trials and composition of the prevention package offered to trial participants remain. The role of advocacy and market research will be crucial to ensure effective interventions are accessed and supported. There is renewed hope in the HIV prevention field with collective efforts needed to ensure we get the new prevention tools and options into the hands of men and women at risk of HIV infection. The purpose of this paper is to provide a review of existing research and identify issues for future enquiry.

Estradiol-Treated Female Mice as Surrogate Hosts for Neisseria gonorrhoeae Genital Tract Infections

Historically, animal modeling of gonorrhea has been hampered by the exclusive adaptation of Neisseria gonorrhoeae to humans. Genital tract infection can be established in female mice that are treated with 17β-estradiol, however, and many features of experimental murine infection mimic human infection. Here we review the colonization kinetics and host response to experimental murine gonococcal infection, including mouse strain differences and evidence that IL-17 responses, toll-like receptor 4, and T regulatory cells play a role in infection. We also discuss the strengths and limitations of the mouse system and the potential of transgenic mice to circumvent host restrictions. Additionally, we review studies with genetically defined mutants that demonstrated a role for sialyltransferase and the MtrC-MtrD-MtrE active efflux pump in evading innate defenses in vivo, but not for factors hypothesized to protect against the phagocytic respiratory burst and H(2)O(2)-producing lactobacilli. Studies using estradiol-treated mice have also revealed the existence of non-host-restricted iron sources in the female genital tract and the influence of hormonal factors on colonization kinetics and selection for opacity (Opa) protein expression. Recent work by others with estradiol-treated mice that are transgenic for human carcinoembryonic adhesion molecules (CEACAMs) supports a role for Opa proteins in enhancing cellular attachment and thus reduced shedding of N. gonorrhoeae. Finally we discuss the use of the mouse model in product testing and a recently developed gonorrhea chlamydia coinfection model.

The potential impact of an HIV vaccine with limited protection on HIV incidence in Thailand: a modeling study

BACKGROUND

The RV144 trial on the ALVAC/AIDSVAX candidate HIV vaccine, carried out in Thailand, showed short-lived protection against infection.

METHODS

Using a deterministic compartmental model we explored the potential impact of this vaccine on heterosexual HIV transmission in Thailand. Both one-off vaccination strategies, as well as strategies with regular boosting, either annually or every two years, were explored. Both targeting the general adult population and prioritizing sex workers were modeled. The impact of risk compensation among high risk groups, as well as whether higher levels of safe sex in high risk groups could be an alternative to vaccination, was studied.

RESULTS

One-off vaccination campaigns had only transient effects, and boosting appears to be a key component of successful vaccination campaigns. Intensive vaccination campaigns may reduce HIV incidence by up to 75% after 10 years of vaccination. Targeting only sex workers has a smaller impact but has a more favorable cost-benefit ratio. Risk compensation has the potential of undoing much of the benefits of a vaccination program and may even increase incidence. In contrast, higher levels of safe sex among sex workers would provide a viable alternative to vaccinating this group.

DISCUSSION

The new vaccine holds promise for controlling HIV in Thailand and similar countries. In view of the short lived protection of the vaccine, regular boosting of immunity as well as avoidance of risk compensation are essential. Targeting sex workers would achieve the greatest reduction in incidence per vaccination and may be considered for expensive vaccines but its cost-effectiveness has to be compared to alternatives.

The rapidly changing paradigm of HIV prevention: time to strengthen social and behavioural approaches

A decade after the world's leaders committed to fight the global HIV epidemic, UNAIDS notes progress in halting the spread of the virus. Access to treatment has in particular increased, with noticeable beneficial effects on HIV-related mortality. Further scaling-up treatment requires substantial human and financial resources and the continued investments that are required may further erode the limited resources for HIV prevention. Treatment can play a role in reducing the transmission of HIV, but treatment alone is not enough and cost-effective behavioural prevention approaches are available that in recent years have received less priority. HIV prevention may in the future benefit from novel biomedical approaches that are in development, including those that capitalize on the use of treatment. To date, evidence of effectiveness of biomedical prevention in real-life conditions is limited and, while they can increase prevention options, many biomedical prevention approaches will continue to rely on the behaviours of individuals and communities. These behaviors are shaped and constrained by the social, cultural, political and economic contexts that affect the vulnerability of individuals and communities. At the start of the 4(th) decade of the epidemic, it is timely to re-focus on strengthening the theory and practice of behavioural prevention of HIV.

HIV prevention research: taking stock and the way forward

Previous papers in this supplement have reviewed the evidence of the effectiveness of alternative HIV prevention methods from randomized controlled trials and other studies. This paper draws together the main conclusions from these reviews. A conceptual framework is presented that maps the proximal and distal determinants of sexual HIV transmission and helps to identify the stages in the causal pathway at which each intervention approach acts. The advances, gaps and challenges emerging from the reviews of individual intervention methods are summarized and cross-cutting themes identified. Approximately 90% of HIV prevention trials have found no effect on HIV incidence and we explore the alternative explanations for the large number of 'flat' trials. We conclude that there is no single explanation for these flat results, which may be due to interventions that are ineffective or inappropriately targeted or implemented, or to factors related to the design or conduct of trials. We examine the lessons from these flat results and provide recommendations on what should be done differently in future trials. HIV prevention remains of critical importance in an era of expanded delivery of antiretroviral therapy. In future HIV prevention research, it is important that resources are used as efficiently as possible to provide rigorous evidence of the effectiveness of a wider array of complementary prevention tools.