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The RTS,S/AS01 - " vaccine has shown consistent but partial vaccine efficacy in a pediatric phase 3 clinical trial using a 3-dose immunization schedule. A fourth-dose 18 months after the primary vaccination was shown to restore the waning efficacy. However, only total IgG against the immunodominant malaria vaccine epitope has been analyzed following the booster. To better characterize the magnitude, nature, and longevity of the immune response to the booster, we measured levels of total IgM, IgG, and IgG" - " subclasses against three constructs of the circumsporozoite protein (CSP) and the hepatitis B surface antigen (HBsAg, also present in RTS,S) by quantitative suspension array technology in 50 subjects in the phase 3 trial in Manhi\xC3\xA7a, Mozambique. To explore the impact of vaccination on naturally acquired immune responses, we measured antibodies to " - " antigens not included in RTS,S. We found increased IgG, IgG1, IgG3 and IgG4, but not IgG2 nor IgM, levels against vaccine antigens 1 month after the fourth dose. Overall, antibody responses to the booster dose were lower than the initial peak response to primary immunization and children had higher IgG and IgG1 levels than infants. Higher anti-Rh5 IgG and IgG" - " levels were detected after the booster dose, suggesting that RTS,S partial protection could increase some blood stage antibody responses. Our work shows that the response to the RTS,S/AS01" - " booster dose is different from the primary vaccine immune response and highlights the dynamic changes in subclass antibody patterns upon the vaccine booster and with acquisition of adaptive immunity to malaria."

Malaria eradication has for decades been on the global health agenda, but the causative agents of the disease, several species of the protist parasite Plasmodium, have evolved mechanisms to evade vaccine-induced immunity and to rapidly acquire resistance against all drugs entering clinical use. Because classical antimalarial approaches have consistently failed, new strategies must be explored. One of these is nanomedicine, the application of manipulation and fabrication technology in the range of molecular dimensions between 1 and 100 nm, to the development of new medical solutions. Here we review the current state of the art in malaria diagnosis, prevention, and therapy and how nanotechnology is already having an incipient impact in improving them. In the second half of this review, the next generation of antimalarial drugs currently in the clinical pipeline is presented, with a definition of these drugs’ target product profiles and an assessment of the potential role of nanotechnology in their development. Opinions extracted from interviews with experts in the fields of nanomedicine, clinical malaria, and the economic landscape of the disease are included to offer a wider scope of the current requirements to win the fight against malaria and of how nanoscience can contribute to achieve them. © 2021 by the authors. Licensee MDPI, Basel, Switzerland.

RTS,S/AS01E has been tested in a phase 3 malaria vaccine study with partial efficacy in African children and infants. In a cohort of 1028 subjects from one low (Bagomoyo) and two high (Nanoro, Kintampo) malaria transmission sites, we analysed IgG plasma/serum concentration and avidity to CSP (NANP-repeat and C-terminal domains) after a 3-dose vaccination against time to clinical malaria events during 12-months. Here we report that RTS,S/AS01E induces substantial increases in IgG levels from pre- to post-vaccination (p, RTS,S/AS01E has been tested in a phase 3 malaria vaccine trial and has shown partial efficacy in children and infants. Here, the authors analyze IgG concentration and avidity to CSP in ~1000 participants and show that IgG avidity to the C-terminus of CSP is significantly associated with vaccine-mediated protection.

Background We assessed the safety and immunogenicity of the RTS,S/AS01 malaria vaccine in a subset of children identified as HIV-infected during a large phase III randomized controlled trial conducted in seven sub-Saharan African countries. Methods Infants 6–12 weeks and children 5–17 months old were randomized to receive 4 RTS,S/AS01 doses (R3R group), 3 RTS,S/AS01 doses plus 1 comparator vaccine dose (R3C group), or 4 comparator vaccine doses (C3C group) at study months 0, 1, 2 and 20. Infants and children with WHO stage III/IV HIV disease were excluded but HIV testing was not routinely performed on all participants; our analyses included children identified as HIV-infected based on medical history or clinical suspicion and confirmed by polymerase chain reaction or antibody testing. Serious adverse events (SAEs) and anti-circumsporozoite (CS) antibodies were assessed. Results Of 15459 children enrolled in the trial, at least 1953 were tested for HIV and 153 were confirmed as HIV-infected (R3R: 51; R3C: 54; C3C: 48). Among these children, SAEs were reported for 92.2% (95% CI: 81.1–97.8) in the R3R, 85.2% (72.9–93.4) in the R3C and 87.5% (74.8–95.3) in the C3C group over a median follow-up of 39.3, 39.4 and 38.3 months, respectively. Fifteen HIV-infected participants in each group (R3R: 29.4%, R3C: 27.8%, C3C: 31.3%) died during the study. No deaths were considered vaccination-related. In a matched case-control analysis, 1 month post dose 3 anti-CS geometric mean antibody concentrations were 193.3 EU/mL in RTS,S/AS01-vaccinated HIV-infected children and 491.5 EU/mL in RTS,S/AS01-vaccinated immunogenicity controls with unknown or negative HIV status (p = 0.0001). Conclusions The safety profile of RTS,S/AS01 in HIV-infected children was comparable to that of the comparator (meningococcal or rabies) vaccines. RTS,S/AS01 was immunogenic in HIV-infected children but antibody concentrations were lower than in children with an unknown or negative HIV status. Clinical trial registration: ClinicalTrials.gov: NCT00866619.

Background. The World Health Organization has recommended pilot implementation of a candidate vaccine against malaria (RTS,S/AS01) in selected sub-Saharan African countries. This exploratory study aimed to estimate the costs of implementing RTS,S in Burkina Faso, Ghana, Kenya, Mozambique, and Tanzania. Methods. Key informants of the expanded program on immunization at all levels in each country were interviewed on the resources required for implementing RTS,S for routine vaccination. Unit prices were derived from the same sources or from international price lists. Incremental costs in 2015 US dollars were aggregated per fully vaccinated child (FVC). It was assumed the four vaccine doses were either all delivered at health facilities or the fourth dose was delivered in an outreach setting. Results. The costs per FVC ranged from US$25 (Burkina Faso) to US$37 (Kenya) assuming a vaccine price of US$5 per dose. Across countries, recurrent costs represented the largest share dominated by vaccines (including wastage) and supply costs. Non-recurrent costs varied substantially across countries, mainly because of differences in needs for hiring personnel, in wages, in cold-room space, and equipment. Recent vaccine introductions in the countries may have had an impact on resource availability for a new vaccine implementation. Delivering the fourth dose in outreach settings raised the costs, mostly fuel, per FVC by less than US$1 regardless of the country. Conclusions. This study provides relevant information for donors and decision makers about the cost of implementing RTS,S. Variations within and across countries are important and the unknown future price per dose and wastage rate for this candidate vaccine adds substantially to the uncertainty about the actual costs of implementation.

Background. The World Health Organization is planning a pilot introduction of a new malaria vaccine in three sub-Saharan African countries. To inform considerations about including a new vaccine in the vaccination program of those and other countries, estimates from the scientific literature of the incremental costs of doing so are important. Methods. A systematic review of scientific studies reporting the costs of recent vaccine programs in sub-Saharan countries was performed. The focus was to obtain from each study an estimate of the cost per dose of vaccine administered excluding the acquisition cost of the vaccine and wastage. Studies published between 2000 and 2018 and indexed on PubMed could be included and results were standardized to 2015 US dollars (US$). Results. After successive screening of 2119 titles, and 941 abstracts, 58 studies with 80 data points (combinations of country, vaccine type, and vaccination approach–routine v. campaign) were retained. Most studies used the so-called ingredients approach as costing method combining field data collection with documented unit prices per cost item. The categorization of cost items and the extent of detailed reporting varied widely. Across the studies, the mean and median cost per dose administered was US$1.68 and US$0.88 with an interquartile range of US$0.54 to US$2.31. Routine vaccination was more costly than campaigns, with mean cost per dose of US$1.99 and US$0.88, respectively. Conclusion. Across the studies, there was huge variation in the cost per dose delivered, between and within countries, even in studies using consistent data collection tools and analysis methods, and including many health facilities. For planning purposes, the interquartile range of US$0.54 to US$2.31 may be a sufficiently precise estimate.

During the intraerythrocytic asexual cycle malaria parasites acquire nutrients and other solutes through a broad selectivity channel localized at the membrane of the infected erythrocyte termed the plasmodial surface anion channel (PSAC). The protein product of the Plasmodium falciparum clonally variant clag3.1 and clag3.2 genes determines PSAC activity. Switches in the expression of clag3 genes, which are regulated by epigenetic mechanisms, are associated with changes in PSAC-dependent permeability that can result in resistance to compounds toxic for the parasite, such as blasticidin S. Here, we investigated whether other antimalarial drugs require CLAG3 to reach their intracellular target and consequently are prone to parasite resistance by epigenetic mechanisms. We found that the bis-thiazolium salts T3 (also known as albitiazolium) and T16 require the product of clag3 genes to enter infected erythrocytes. P. falciparum populations can develop resistance to these compounds via the selection of parasites with dramatically reduced expression of both genes. However, other compounds previously demonstrated or predicted to enter infected erythrocytes through transport pathways absent from noninfected erythrocytes, such as fosmidomycin, doxycycline, azithromycin, lumefantrine, or pentamidine, do not require expression of clag3 genes for their antimalarial activity. This suggests that they use alternative CLAG3-independent routes to access parasites. Our results demonstrate that P. falciparum can develop resistance to diverse antimalarial compounds by epigenetic changes in the expression of clag3 genes. This is of concern for drug development efforts because drug resistance by epigenetic mechanisms can arise quickly, even during the course of a single infection.

Background Today, the development of new and well-tolerated anti-malarial drugs is strongly justified by the emergence of Plasmodium falciparum resistance. In 2014–2015, a phase 2b clinical study was conducted to evaluate the efficacy of a single oral dose of Artefenomel (OZ439)–piperaquine (PPQ) in Asian and African patients presenting with uncomplicated falciparum malaria. Methods Blood samples collected before treatment offered the opportunity to investigate the proportion of multidrug resistant parasite genotypes, including P. falciparum kelch13 mutations and copy number variation of both P. falciparum plasmepsin 2 (Pfpm2) and P. falciparum multidrug resistance 1 (Pfmdr1) genes. Results Validated kelch13 resistance mutations including C580Y, I543T, P553L and V568G were only detected in parasites from Vietnamese patients. In Africa, isolates with multiple copies of the Pfmdr1 gene were shown to be more frequent than previously reported (21.1%, range from 12.4% in Burkina Faso to 27.4% in Uganda). More strikingly, high proportions of isolates with multiple copies of the Pfpm2 gene, associated with piperaquine (PPQ) resistance, were frequently observed in the African sites, especially in Burkina Faso and Uganda (> 30%). Conclusions These findings were considered to sharply contrast with the recent description of increased sensitivity to PPQ of Ugandan parasite isolates. This emphasizes the necessity to investigate in vitro susceptibility profiles to PPQ of African isolates with multiple copies of the Pfpm2 gene and estimate the risk of development of PPQ resistance in Africa. Trial registration Clinicaltrials.gov reference: NCT02083380. Study title: Phase II efficacy study of artefenomel and piperaquine in adults and children with P. falciparum malaria. https://clinicaltrials.gov/ct2/results?cond=&term=NCT02083380&cntry=&state=&city=&dist=. FSFV: 23-Jul-2014; LSLV: 09-Oct-2015

Biomaterials for antimalarial drug transport still need to be investigated in order to attain nanocarriers that can tackle essential issues related to malaria treatment, e.g. complying with size requirements and targeting specificity for their entry into Plasmodium-infected red blood cells (pRBCs), and limiting premature drug elimination or drug resistance evolution. Two types of dendritic macromolecule that can form vehicles suitable for antimalarial drug transport are herein explored. A new hybrid dendritic-linear-dendritic block copolymer based on Pluronic® F127 and amino terminated 2,2′-bis(glycyloxymethyl)propionic acid dendrons with a poly(ester amide) skeleton (HDLDBC-bGMPA) and an amino terminated dendronized hyperbranched polymer with a polyester skeleton derived from 2,2′-bis(hydroxymethyl)propionic acid (DHP-bMPA) have provided self-assembled and unimolecular micelles. Both types of micelle carrier are biocompatible and exhibit appropriate sizes to enter into pRBCs. Targeting studies have revealed different behaviors for each nanocarrier that may open new perspectives for antimalarial therapeutic approaches. Whereas DHP-bMPA exhibits a clear targeting specificity for pRBCs, HDLDBC-bGMPA is incorporated by all erythrocytes. It has also been observed that DHP-bMPA and HDLDBC-bGMPA incorporate into human umbilical vein endothelial cells with different subcellular localization, i.e. cytosolic and nuclear, respectively. Drug loading capacity and encapsulation efficiencies for the antimalarial compounds chloroquine, primaquine and quinacrine ranging from 30% to 60% have been determined for both carriers. The resulting drug-loaded nanocarriers have been tested for their capacity to inhibit Plasmodium growth in in vitro and in vivo assays., This research was supported by grants BIO2014-52872-R, CTQ2015-70174-P, MAT2015-66208-C3-1-P (Ministerio de Ciencia, Innovación y Universidades, Spain, including FEDER funds), 2014-SGR-938 (Generalitat de Catalunya, Spain), and (Gobierno de Aragón-FSE). ISGlobal and IBEC are members of the CERCA Programme, Generalitat de Catalunya. A. L. thanks the Ministerio de Ciencia, Innovación y Universidades for his grant (FPU12/05210). L. N. B.-C. is supported by the European Commission under Horizon 2020's Marie Skłodowska-Curie Actions COFUND scheme (Grant Agreement no. 712754) and by the MINECO's Severo Ochoa programme (Grant SEV-2014-0425 (2015–2019))., The authors acknowledge support of the publication fee by the CSIC Open Access Publication Support Initiative through its Unit of Information Resources for Research (URICI).

Background Leading malaria vaccine, RTS,S, is based on the circumsporozoite protein (CSP) of sporozoites. RTS,S confers partial protection against malaria in children, but efficacy wanes relatively quickly after primary immunization. Vaccine efficacy has some association with anti-CSP IgG; however, it is unclear how these antibodies function, and how functional antibodies are induced and maintained over time. Recent studies identified antibody-complement interactions as a potentially important immune mechanism against sporozoites. Here, we investigated whether RTS,S vaccine-induced antibodies could function by interacting with complement. Methods Serum samples were selected from children in a phase IIb trial of RTS,S/AS02A conducted at two study sites of high and low malaria transmission intensity in Manhiça, Mozambique. Samples following primary immunization and 5-year post-immunization follow-up time points were included. Vaccine-induced antibodies were characterized by isotype, subclass, and epitope specificity, and tested for the ability to fix and activate complement. We additionally developed statistical methods to model the decay and determinants of functional antibodies after vaccination. Results RTS,S vaccination induced anti-CSP antibodies that were mostly IgG1, with some IgG3, IgG2, and IgM. Complement-fixing antibodies were effectively induced by vaccination, and targeted the central repeat and C-terminal regions of CSP. Higher levels of complement-fixing antibodies were associated with IgG that equally recognized both the central repeat and C-terminal regions of CSP. Older age and higher malaria exposure were significantly associated with a poorer induction of functional antibodies. There was a marked decay in functional complement-fixing antibodies within months after vaccination, as well as decays in IgG subclasses and IgM. Statistical modeling suggested the decay in complement-fixing antibodies was mostly attributed to the waning of anti-CSP IgG1, and to a lesser extent IgG3. Conclusions We demonstrate for the first time that RTS,S can induce complement-fixing antibodies in young malaria-exposed children. The short-lived nature of functional responses mirrors the declining vaccine efficacy of RTS,S over time. The negative influence of age and malaria exposure on functional antibodies has implications for understanding vaccine efficacy in different settings. These findings provide insights into the mechanisms and longevity of vaccine-induced immunity that will help inform the future development of highly efficacious and long-lasting malaria vaccines. Electronic supplementary material The online version of this article (10.1186/s12916-019-1277-x) contains supplementary material, which is available to authorized users.

A phase III, double-blind, randomized, controlled trial (NCT00866619) in sub-Saharan Africa showed RTS,S/AS01 vaccine efficacy against malaria. We now present in-depth safety results from this study. 8922 children (enrolled at 5-17\xC2\xA0months) and 6537 infants (enrolled at 6-12\xC2\xA0weeks) were 1:1:1-randomized to receive 4 doses of RTS,S/AS01 (R3R) or non-malaria control vaccine (C3C), or 3 RTS,S/AS01 doses plus control (R3C). Aggregate safety data were reviewed by a multi-functional team. Severe malaria with Blantyre Coma Score \xE2\x89\xA42 (cerebral malaria [CM]) and gender-specific mortality were assessed post-hoc. Serious adverse event (SAE) and fatal SAE incidences throughout the study were 24.2%-28.4% and 1.5%-2.5%, respectively across groups; 0.0%-0.3% of participants reported vaccination-related SAEs. The incidence of febrile convulsions in children was higher during the first 2-3 days post-vaccination with RTS,S/AS01 than with control vaccine, consistent with the time window of post-vaccination febrile reactions in this study (mostly the day after vaccination). A statistically significant numerical imbalance was observed for meningitis cases in children (R3R: 11, R3C: 10, C3C: 1) but not in infants. CM cases were more frequent in RTS,S/AS01-vaccinated children (R3R: 19, R3C: 24, C3C: 10) but not in infants. All-cause mortality was higher in RTS,S/AS01-vaccinated versus control girls (2.4% vs 1.3%, all ages) in our setting with low overall mortality. The observed meningitis and CM signals are considered likely chance findings, that - given their severity - warrant further evaluation in phase IV studies and WHO-led pilot implementation programs to establish the RTS,S/AS01 benefit-risk profile in real-life settings.

Vaccines are, indisputably, one of the greatest public health interventions, with a substantial positive impact on child survival. The remarkable declines in child mortality observed during the last quarter of a century, whereby global under 5 deaths were essentially halved, go hand in hand with the estimated 2–3 million child deaths prevented by vaccines annually.1 The premise for this is clear: vaccines directly prevent a variety of life-threatening diseases. Vaccines can also be held directly responsible for the eradication of smallpox, the first and only infectious disease extinguished by the action of humans and are paving the way for the disappearance of other terrible infections such as polio, measles or rubella. In recent years, however, it has become increasingly clear that the impact of vaccines is achieved by their direct prevention against specific pathogens, and through a series of non-specific effects.2 These non-specific effects, also termed ‘heterologous’ effects, appear to be more common as a result of the vaccination with certain live-attenuated antigens (eg, the Bacillus Calmette-Guerin (BCG), measles or polio), and have been proposed for a wide variety of existing vaccines. Observational studies have pointed out to a longer-term all-cause mortality decrease attributable to having received those vaccines, independent of the target disease. Non-specific effects are understandably less tangible and less well-characterised than the direct ones, and therefore, remain a matter of significant debate and controversy.3 To date, the nature of non-specific effects has not been fully elucidated, although the current thinking points to trained innate immunity as the main underlying mechanism.4 Trained immunity refers to an immunological memory of the innate response, a process in which certain stimuli induce epigenetic changes in the innate immune cells,5 increasing the response to the same and different subsequent stimuli. Vaccines with non-specific effects would induce reprogramming of …

BACKGROUND: At a World Health Organization (WHO) sponsored meeting it was concluded that there is an urgent need for a reference preparation that contains antibodies against malaria antigens in order to support serology studies and vaccine development. It was proposed that this reference would take the form of a lyophilized serum or plasma pool from a malaria-endemic area. In response, an immunoassay standard, comprising defibrinated human plasma has been prepared and evaluated in a collaborative study. RESULTS: A pool of human plasma from a malaria endemic region was collected from 140 single plasma donations selected for reactivity to Plasmodium falciparum apical membrane antigen-1 (AMA-1) and merozoite surface proteins (MSP-119, MSP-142, MSP-2 and MSP-3). This pool was defibrinated, filled and freeze dried into a single batch of ampoules to yield a stable source of naturally occurring antibodies to P. falciparum. The preparation was evaluated by an enzyme-linked immunosorbent assay (ELISA) in a collaborative study with sixteen participants from twelve different countries. This anti-malaria human serum preparation (NIBSC Code: 10/198) was adopted by the WHO Expert Committee on Biological Standardization (ECBS) in October 2014, as the first WHO reference reagent for anti-malaria (Plasmodium falciparum) human serum with an assigned arbitrary unitage of 100 units (U) per ampoule. CONCLUSION: Analysis of the reference reagent in a collaborative study has demonstrated the benefit of this preparation for the reduction in inter- and intra-laboratory variability in ELISA. Whilst locally sourced pools are regularly use for harmonization both within and between a few laboratories, the presence of a WHO-endorsed reference reagent should enable optimal harmonization of malaria serological assays either by direct use of the reference reagent or calibration of local standards against this WHO reference. The intended uses of this reference reagent, a multivalent preparation, are (1) to allow cross-comparisons of results of vaccine trials performed in different centres/with different products; (2) to facilitate standardization and harmonization of immunological assays used in epidemiology research; and (3) to allow optimization and validation of immunological assays used in malaria vaccine development.

[eng] The process of creating an efficacious malaria vaccine is complex due to the characteristics of the disease that are directly related to the responsible parasite. In the disease-vaccine interaction several aspects need to be taken into account to improve and understand the vaccine and for that reason different types of data need to be analyzed. Current assays technology allows analyzing several proteins simultaneously with a small blood volume. The combination of the medium throughput dataset of some assays and the small sample size of some malaria studies may hinder the use of classical statistical methods. In the context of low number of observations and medium or high number of variables the support vector machines (SVM) models are a powerful tool to analyze sparse data, i.e., data in which the number of predictors is larger or approximately equal to the number of observations, especially when handling binary outcomes. However, biomedical research often involves analysis of time-to-event outcomes. Several methods have been tested in the literature to deal with censored data into the SVM framework. Most of these methods are based on a support vector regression (SVR) approach and results found in the literature suggest no significant differences with Cox proportional hazards model and kernel Cox regression. Another perspective is a SVM for binary classification, however, almost no work has been done into this approach: only SVM learning using privileged information and SVM with uncertain classes have been described. This PhD thesis aims to propose alternative methods and extensions to the ones existing in the binary classification framework, specifically, proposing a conditional survival approach for weighting censored observations, a semi-supervised SVM with local invariances perspective and evaluating a weighted SVM model. Another important aspect in biomedical research is to identify the relevance of the variables in a model, i.e., which variables are important related to the response variable. In the SVM framework most of the work done is related to linear kernels, however, the main advantage of SVM is using non-linear kernels. This PhD thesis aims to propose three approaches based on the Recursive Feature Elimination (RFE) algorithm to rank variables based on non-linear SVM and SVM for survival analysis. Moreover, the proposed algorithms are focused on interpretation and visualization of each one the RFE iterations, allowing to identify relevant variables associated with the response variable and among predictor variables. After evaluating all proposed methods in a simulation study under several scenarios, a real dataset applying these methods has been analyzed: the Mal067 data aims to identify immune responses correlated with protection from malaria that were elicited by the malaria RTS,S vaccine and by natural immunity. All SVM for survival analysis methods have been implemented in R, since neither R packages nor R functions have been found., [cat] El procés de crear una vacuna eficaç contra la malària és complex degut a les característiques del paràsit responsable. Les tècniques de laboratori actuals permeten analitzar moltes proteïnes simultàniament amb molt poc volum de sang, això, juntament amb la poca grandària mostral de molts estudis de malària fa que els mètodes estadístics clàssics no siguin adequats. Les màquines de suport vectorial (SVM) són una eina molt potent per tractar aquest tipus de dades en el context de poques observacions i moltes variables, moltes vegades, però, la recerca està enfocada en variables resposta temps fins a esdeveniment. Gran part de la recerca feta a la literatura en aproximar els mètodes SVM a dades de supervivència està enfocada des de la perspectiva de SVM per regressió. Una altra perspectiva molt poc desenvolupada i avaluada és la de SVM per classificació binària. En aquesta tesi proposem extensions i mètodes alternatius basats en SVM per classificació binària, específicament, proposant una ponderació de les dades censurades basada en la supervivència condicionada, una perspectiva semi-supervisada de SVM amb invariàncies locals i l’avaluació de SVM ponderant les observacions censurades. Un aspecte important en la recerca biomèdica és la identificació de la rellevància de variables en el model, és a dir, quines variables són importants en relació a la variable resposta. En el context de SVM, gran part de la recerca està enfocada a kernels lineals, però el gran avantatge dels SVM és la possibilitat d’utilitzar kernels no lineals. En aquesta tesi proposem tres aproximacions basades en l’algoritme recursiu d’eliminació de característiques (RFE) per ordenar variables, des d’una perspectiva de kernels no lineals i SVM per l’anàlisi de supervivència. A més, els mètodes proposats permeten ser interpretats i visualitzats a cada iteració de l’algoritme RFE, permeten identificar la rellevància de les variables predictores amb respecte la variable resposta i l’associació entre variables predictores. Després d’avaluar tots els mètodes proposats per SVM amb dades censurades i rellevància de variables, mitjançant simulacions, s’han analitzat les dades reals de l’estudi Mal067 que estudia correlats de protecció contra la malària induïts per la vacuna RTS,S.

Novel antimalarial therapies are needed in the face of emerging resistance to artemisinin combination therapies. A previous study found a high cure rate in Mozambican children with uncomplicated Plasmodium falciparum malaria 7 days post treatment with a fosmidomycin-clindamycin combination. However, 28-day cure rates were low (45.9%), due to parasite recrudescence. We sought to identify any genetic changes underlying parasite recrudescence. To this end, we utilized a selective whole genome amplification method to amplify parasite genomes from blood spot DNA samples. Parasite genomes from pre-treatment and post-recrudescence samples were subjected to whole genome sequencing to identify nucleotide variants. We find that our data do not support the existence of a genetic change responsible for recrudescence following fosmidomycin-clindamycin treatment. Additionally, we find that previously described resistance alleles for these drugs do not represent biomarkers of recrudescence. Future studies should continue to optimize fosmidomycin combinations for use as antimalarial therapies.

BACKGROUND: Within the context of combined interventions, malaria vaccine may provide additional value in malaria prevention. Stakeholders' perspectives are thus critical for informed recommendation of the vaccine in Tanzania. This paper presents the views of stakeholders with regards to malaria vaccine in 12 Tanzanian districts. METHODS: Quantitative and qualitative methods were employed. A structured questionnaire was administered to 2123 mothers of under five children. Forty-six in-depth interviews and 12 focus group discussions were conducted with teachers, religious leaders, community health workers, health care professionals, and scientists. Quantitative data analysis involved frequency distributions and cross tabulations using Chi square test to determine the association between malaria vaccine acceptability and independent variables. Qualitative data were analysed thematically. RESULTS: Overall, 84.2 % of the mothers had perfect acceptance of malaria vaccine. Acceptance varied significantly according to religion, occupation, tribe and region (p < 0.001). Ninety two percent reported that they will accept the malaria vaccine despite the need to continue using insecticide-treated nets (ITNs), while 88.4 % reported that they will accept malaria vaccine even if their children get malaria less often than non-vaccinated children. Qualitative results revealed that the positive opinions towards malaria vaccine were due to a need for additional malaria prevention strategies and expectations that the vaccine will reduce visits to the health facility, deaths, malaria episodes and treatment-related expenses. Vaccine related questions included its side effects, efficacy, protective duration, composition, interaction with other medications, provision schedule, availability to the pregnant women, mode of administration (oral or injection?) and whether a child born of HIV virus or with a chronic illness will be eligible for the vaccine? CONCLUSION: Stakeholders had high acceptance and positive opinions towards the combined use of the anticipated malaria vaccine and ITNs, and that their acceptance remains high even when the vaccine may not provide full protection, this is a crucial finding for malaria vaccine policy decisions in Tanzania. An inclusive communication strategy should be designed to address the stakeholders' questions through a process that should engage and be implemented by communities and health care professionals. Social cultural aspects associated with vaccine acceptance should be integrated in the communication strategy.

Sanaria Inc. has developed methods to manufacture, purify and cryopreserve aseptic Plasmodium falciparum (Pf) sporozoites (SPZ), and is using this platform technology to develop an injectable PfSPZ-based vaccine that provides high-grade, durable protection against infection with Pf malaria. Several candidate vaccines are being developed and tested, including PfSPZ Vaccine, in which the PfSPZ are attenuated by irradiation, PfSPZ-CVac, in which fully infectious PfSPZ are attenuated in vivo by concomitant administration of an anti-malarial drug, and PfSPZ-GA1, in which the PfSPZ are attenuated by gene knockout. Forty-three research groups in 15 countries, organized as the International PfSPZ Consortium (I-PfSPZ-C), are collaborating to advance this program by providing intellectual, clinical, and financial support. Fourteen clinical trials of these products have been completed in the USA, Europe and Africa, two are underway and at least 12 more are planned for 2015-2016 in the US (four trials), Germany (2 trials), Tanzania, Kenya, Mali, Burkina Faso, Ghana and Equatorial Guinea. Sanaria anticipates application to license a first generation product as early as late 2017, initially to protect adults, and a year later to protect all persons >6 months of age for at least six months. Improved vaccine candidates will be advanced as needed until the following requirements have been met: long-term protection against natural transmission, excellent safety and tolerability, and operational feasibility for population-wide administration. Here we describe the three most developed whole PfSPZ vaccine candidates, associated clinical trials, initial plans for licensure and deployment, and long-term objectives for a final product suitable for mass administration to achieve regional malaria elimination and eventual global eradication.

BACKGROUND: The RTS,S/AS01 malaria vaccine targets the circumsporozoite protein, inducing antibodies associated with the prevention of Plasmodium falciparum infection. We assessed the association between anti-circumsporozoite antibody titres and the magnitude and duration of vaccine efficacy using data from a phase 3 trial done between 2009 and 2014. METHODS: Using data from 8922 African children aged 5-17 months and 6537 African infants aged 6-12 weeks at first vaccination, we analysed the determinants of immunogenicity after RTS,S/AS01 vaccination with or without a booster dose. We assessed the association between the incidence of clinical malaria and anti-circumsporozoite antibody titres using a model of anti-circumsporozoite antibody dynamics and the natural acquisition of protective immunity over time. FINDINGS: RTS,S/AS01-induced anti-circumsporozoite antibody titres were greater in children aged 5-17 months than in those aged 6-12 weeks. Pre-vaccination anti-circumsporozoite titres were associated with lower immunogenicity in children aged 6-12 weeks and higher immunogenicity in those aged 5-17 months. The immunogenicity of the booster dose was strongly associated with immunogenicity after primary vaccination. Anti-circumsporozoite titres wane according to a biphasic exponential distribution. In participants aged 5-17 months, the half-life of the short-lived component of the antibody response was 45 days (95% credible interval 42-48) and that of the long-lived component was 591 days (557-632). After primary vaccination 12% (11-13) of the response was estimated to be long-lived, rising to 30% (28-32%) after a booster dose. An anti-circumsporozoite antibody titre of 121 EU/mL (98-153) was estimated to prevent 50% of infections. Waning anti-circumsporozoite antibody titres predict the duration of efficacy against clinical malaria across different age categories and transmission intensities, and efficacy wanes more rapidly at higher transmission intensity. INTERPRETATION: Anti-circumsporozoite antibody titres are a surrogate of protection for the magnitude and duration of RTS,S/AS01 efficacy, with or without a booster dose, providing a valuable surrogate of effectiveness for new RTS,S formulations in the age groups considered. FUNDING: UK Medical Research Council.

BACKGROUND: Controlled human malaria infection (CHMI) by mosquito bite is a powerful tool for evaluation of vaccines and drugs against Plasmodium falciparum malaria. However, only a small number of research centres have the facilities required to perform such studies. CHMI by needle and syringe could help to accelerate the development of anti-malaria interventions by enabling centres worldwide to employ CHMI. METHODS: An open-label CHMI study was performed with aseptic, purified, cryopreserved P. falciparum sporozoites (PfSPZ Challenge) in 36 malaria naive volunteers. In part A, the effect of the inoculation volume was assessed: 18 participants were injected intramuscularly (IM) with a dose of 2,500 PfSPZ divided into two injections of 10 microL (n = 6), 50 microL (n = 6) or 250 microL (n = 6), respectively. In part B, the injection volume that resulted in highest infectivity rates in part A (10 microL) was used to formulate IM doses of 25,000 PfSPZ (n = 6) and 75,000 PfSPZ (n = 6) divided into two 10-microL injections. Results from a parallel trial led to the decision to add a positive control group (n = 6), each volunteer receiving 3,200 PfSPZ in a single 500-microL injection by direct venous inoculation (DVI). RESULTS: Four/six participants in the 10-microL group, 1/6 in the 50-microL group and 2/6 in the 250-microL group developed parasitaemia. Geometric mean (GM) pre-patent periods were 13.9, 14.0 and 15.0 days, respectively. Six/six (100%) participants developed parasitaemia in the 25,000 and 75,000 PfSPZ IM and 3,200 PfSPZ DVI groups. GM pre-patent periods were 12.2, 11.4 and 11.4 days, respectively. Injection of PfSPZ Challenge was well tolerated and safe in all groups. CONCLUSIONS: IM injection of 75,000 PfSPZ and DVI injection of 3,200 PfSPZ resulted in infection rates and pre-patent periods comparable to the bite of five PfSPZ-infected mosquitoes. Remarkably, it required 23.4-fold more PfSPZ administered IM than DVI to achieve the same parasite kinetics. These results allow for translation of CHMI from research to routine use, and inoculation of PfSPZ by IM and DVI regimens. TRIAL REGISTRATION: ClinicalTrials.gov NCT01771848.

Malaria remains a major cause of mortality and morbidity worldwide. Progress has been made in recent years with the development of vaccines that could pave the way towards protection of hundreds of millions of exposed individuals. Here we used a modular repertoire approach to re-analyze a publically available microarray blood transcriptome dataset monitoring the response to malaria vaccination. We report the seminal identification of interferon signatures in the blood of subjects on days 1, 3 and 14 following administration of the third dose of the RTS,S recombinant malaria vaccine. These signatures at day 1 correlate with protection, and at days 3 and 14 to susceptibility to subsequent challenge of study subjects with live parasites. In addition we putatively link the decreased abundance of interferon-inducible transcripts observed at days 3 and 14 post-vaccination with the elicitation of an antigen-specific IgE response in a subset of vaccine recipients that failed to be protected by the RTS,S vaccine. Furthermore, profiling of antigen-specific levels of IgE in a Mozambican cohort of malaria-exposed children vaccinated with RTS,S identified an association between elevated baseline IgE levels and subsequent development of naturally acquired malaria infection during follow up. Taken together these findings warrant further investigation of the role of antigen-specific IgE in conferring susceptibility to malaria infection.

The Papua New Guinea (PNG) Department of Health introduced a 'test and treat' malaria case management protocol in 2011. This study assesses health worker compliance with the test and treat protocol on a wide range of measures, examines self-reported barriers to health worker compliance as well as health worker attitudes towards the test and treat protocol. Data were collected by cross-sectional survey conducted in randomly selected primary health care facilities in 2012 and repeated in 2014. The combined survey data included passive observation of current or recently febrile patients (N = 771) and interviewer administered questionnaires completed with health workers (N = 265). Across the two surveys, 77.6% of patients were tested for malaria infection by rapid diagnostic test (RDT) or microscopy, 65.6% of confirmed malaria cases were prescribed the correct antimalarials and 15.3% of febrile patients who tested negative for malaria infection were incorrectly prescribed an antimalarial. Overall compliance with a strictly defined test and treat protocol was 62.8%. A reluctance to test current/recently febrile patients for malaria infection by RDT or microscopy in the absence of acute malaria symptoms, reserving recommended antimalarials for confirmed malaria cases only and choosing to clinically diagnose a malaria infection, despite a negative RDT result were the most frequently reported barriers to protocol compliance. Attitudinal support for the test and treat protocol, as assessed by a nine-item measure, improved across time. In conclusion, health worker compliance with the full test and treat malaria protocol requires improvement in PNG and additional health worker support will likely be required to achieve this. The broader evidence base would suggest any such support should be delivered over a longer period of time, be multi-dimensional and multi-modal.

Malaria has a high toll on the lives of infants and children under the age of five in endemic areas. Control, and more recently, elimination agendas consist on implementing several measures simultaneously, including vector control, vaccines and drugs. The current Millenium Development Goals aim at reducing malaria mortality and morbidity in the two most vulnerable groups: pregnant women and children. Intermittent Preventive Treatment in Infants with Sulphadoxine‐Pyrimethamine (IPTi-SP) delivered through routine EPI vaccination programs has shown to be efficacious in different transmission settings and the WHO has recently recommended its implementation as a malaria control tool. However, one of the main concerns has been the potential impairment of acquisition of naturally acquired immunity, and this could be a concern regarding IPTi. This thesis reports on a series of studies conducted in a malaria endemic area of Manhiça, Mozambique, to assess the impact of IPTi‐SP on the development of immune responses to the Plasmodium falciparum parasite. In this work, we measured antibody and cellular immune parameters considered to be the most appropriate markers of protective immunity against malaria identified to date. The most consistent finding was that IPTi-SP does not modify the magnitude of the immune responses acquired over the first two years of age in Mozambican children. In addition, we described the factors that affect the antibody and cellular immune responses, and reported those that correlated with prospective malaria incidence. Based on the studies presented herein, we can conclude that IPTi‐SP does not interfere with immune responses that are considered major contributors to the acquisition of protective immunity to malaria in early infancy. In summary, this thesis contributes to a more complete assessment of IPTi as a control measure that will possibly be implemented in the near future in malaria endemic areas of Africa and of the world. In addition, it aims to contribute to advance the knowledge on the acquisition of natural immunity in infancy which is poorly understood. Furthermore, this information will help to understand the factors that should be taken into account when designing and deploying other control measures for this age group.

Malaria, caused by Plasmodium falciparum parasites remains a huge public health problem and a major cause of morbidity and mortality in sub-Saharan Africa, especially among children and infants. The parasite and its vector – the Anopheles spp mosquito - have tremendous adaptability capacities, including the acquisition of resistance to anti-malarial drugs and insecticides, making the development of new preventive tools, such as a safe and effective vaccine, a key element to counter balance this tendency. The most advanced malaria vaccine candidate, RTS,S/AS has progressed to a Phase III trial through a research and development plan as a result of an unforeseen partnership between African, European and American research institutions together with GSK Biologicals and the PATH Malaria Vaccine Initiative (MVI). This thesis describes some critical stages of the clinical development plan of this vaccine, reporting clinical trials of the RTS/AS candidate malaria vaccine conducted in Mozambican children and infants. Here we illustrates the assessment of the RTS,S/AS02D safety, humoral and cellular mediated immune responses and the duration of protection over a one year period in infants. We also provide a detailed immunogenicity data of 4 years of follow-up of children aged 1 to 4 years by the time of immunization with RTS,S/AS02A. These studies principally show that the vaccine is safe, well tolerated and highly immunogenic, eliciting both humoral and cell-mediated antibodies. The vaccine also protects children and infants against clinical malaria. Importantly, they also describe for the first time an association between the risk of clinical malaria and Plasmodium falciparum anticircumsporozoite antibody titters. The presented results support the hypothesis that developing a safe, immunogenic and efficacious malaria vaccine is feasible and, together with other studies, they should be the basis for the registry process of what should be the first generation of vaccines against malaria., La malaria, causada por el parásito Plasmodium falciparum sigue siendo un gran problema de salud pública y una causa importante de mortalidad y morbilidad en el África Sub-Sahariana, especialmente entre los niños y lactantes. El parásito y su vector mosquito Anofeles spp. tienen una tremenda capacidad de adaptación, incluyendo la capacidad de adquirir resistencia a los fármacos antipalúdicos e insecticidas. Es por tanto prioritario desarrollar nuevas herramientas preventivas, entre las cuales una vacuna segura y eficaz, un elemento clave para contrarrestar esta tendencia. La vacuna candidata contra la malaria más avanzada, denominada RTS,S/AS, ha progresado hasta un ensayo de Fase III siguiendo un plan de investigación y desarrollo clínico resultado de una colaboración sin precedentes entre centros de investigación Africanos, Europeos y Americanos junto con la GSK Biologicals y PATH Malaria Vaccine Initiative (MVI). Esta tesis describe algunas de las fases críticas de estos logros, reportando los ensayos clínicos de la vacuna candidata contra la malaria RTS,S/AS llevados a cabo en niños y lactantes de Mozambique. Esta tesis analiza en detalle la evaluación de la seguridad de esta estrategia, la respuesta inmunológica (tanto humoral como celular) que esta vacuna confiere, y la duración de la protección durante un período de seguimiento de un año en los lactantes. Presentamos también los datos completos de 4 años de seguimiento de la inmunogenicidad de la RTS,S/AS02A administrada a niños de 1 a 4 años de edad en el momento de su primera vacunación. Estos estudios demuestran que la vacuna es segura, bien tolerada y altamente inmunogénica, produciendo respuestas tanto humorales como celulares. La vacuna también protege a los niños y lactantes contra la malaria clínica. Además se describe por primera vez una asociación entre el riesgo de malaria clínica y los niveles de anticuerpos contra la proteína de circumsporozoito del Plasmodium falciparum. Los resultados aquí presentados apoyan la tesis de que el desarrollo de una vacuna eficaz, inmunogénica y segura contra la malaria es posible, y deberá ser la base, junto con otros estudios, del proceso de registro de la que podrá ser la primera generación de vacunas contra la malaria.

Despite a renewed impetus on bringing together efforts to wipe malaria from the globe, the truth is that this ancient disease remains one of the principal threats to child survival in vast areas of the world. The existing control measures are largely insufficient to reduce globally the malaria burden, and as of today, malaria remains endemic in more than 100 countries, where at least half of the world's population live exposed to the risk of being infected. Indeed, the burden of malaria morbidity and mortality continues to be unacceptably high, with more than 250 million clinical episodes and at least one million deaths per year. While morbidity due to malaria affects all age groups and is scattered throughout the world, Sub-Saharan Africa concentrates the brunt of the malaria deaths, which overwhelmingly occur in children under five years of age infected with P. falciparum. The exciting and almost palpable perspective of an effective malaria vaccine, added to the promotion of innovative control strategies such as intermittent preventive treatment for infants or pregnant women, have in the recent years centred the scientific discussions regarding the approach to malaria control. However, in contrast to these innovative perspectives, malaria control has remained in the last two decades essentially dependent on the early identification and prompt treatment of clinical malaria cases and the reduction of man-vector contact. Unless there is a major renewal, optimisation and scale-up of the antimalarial arsenal and strategies, malaria will continue to dictate the health status of the world, and eradication will not be achievable in a realistic timeframe. As malaria is a life-threatening infection, a fundamental requirement for its adequate control is the availability of effective antimalarial drugs. The first paper in this thesis describes a large randomised clinical trial (around 1500 children) performed in five different African countries to assess the non-inferiority of a novel combination, dihydroartemisinin-piperaquine, produced under strict good manufacturing practices, when compared to the standard combination therapy AL, for the treatment of uncomplicated malaria in African children under the age of five years. In the second paper, we describe the results of another large (around 900 patients) randomised clinical trial in which we assessed in 5 different African countries the non-inferiority of a new, paediatric-suited cherry-flavoured, dispersible formulation of AL, when compared to standard crushed AL tablets, for the treatment of uncomplicated malaria in children younger than 12 years of age. The results of these two trials, reflected in paper 1 and paper 2 of this thesis, bring to the malaria community public-health relevant data on alternatives to the currently limited antimalarial drug arsenal. The third paper in this thesis describes the clinical presentation of severe malaria in a rural Mozambican Hospital, and the associated risk factors for a negative outcome. It also presents minimum community based incidence rates, a useful indicator of the malaria burden in the area. Finally, the fourth paper addresses the relationship between severe malaria and bacterial invasive disease in children younger than 5 years admitted to a Manhiça's rural hospital, Mozambique. Malaria is an ancient disease of terrible consequences for mankind. All efforts devised to diminish the burden that malaria imposes in endemic areas need to be embraced and brought together on a coordinated manner to fight this infection from all possible fronts. Understanding the clinical determinants of the infection and its relation with other coexistent infectious diseases will give an insight to the basic pathophysiology of malaria, and thus guide appropriate management strategies. New highly effective drugs, and their paediatric-orientated formulations, need to be developed and made available to those most at need., A pesar del renovado afán por eliminar la malaria de la faz de la tierra, esta histórica enfermedad se mantiene como uno de los principales peligros para la salud infantil en amplias zonas del mundo. Las medidas de control existentes son claramente insuficientes a la hora de reducir globalmente el impacto de esta enfermedad, y a día de hoy la malaria es endémica en más de 100 países en dónde más de la mitad de la población mundial está expuesta al riesgo de infectarse. De hecho, la carga de esta enfermedad en términos de morbilidad y mortalidad persiste inaceptablemente alta con, anualmente, más de 250 millones de episodios clínicos y cerca de un millón de muertes. Mientras que la enfermedad clínica puede afectar a cualquier grupo de edad, la mortalidad por malaria se ve esencialmente circunscrita a los niños menores de cinco años infectados por P. falciparum.La apasionante y casi palpable perspectiva de una vacuna efectiva contra la malaria, sumada a la promoción de innovadoras estrategias de control como el tratamiento intermitente en lactantes o mujeres embarazadas han centrado, en los últimos años, el debate científico relacionado con las estrategias de control. En contraste con estas innovadoras estrategias, el control de la malaria se ha visto sin embargo limitado en las últimas décadas a la identificación y tratamiento precoz de los episodios clínicos y a la reducción del contacto entre el reservorio humano y el vector. A menos que se produzca una importante renovación y optimización del arsenal terapéutico y de las estrategias frente a esta infección, acompañado por un despliegue masivo de las intervenciones en aquellas áreas dónde son más necesarias, la malaria continuará dictando el estado de salud global, y su erradicación no dejará de ser una utopía irrealizable a corto plazo.La malaria es una enfermedad potencialmente mortal, y por lo tanto, un requerimiento fundamental para su control es la disponibilidad de fármacos antimaláricos efectivos para su tratamiento. El desarrollo de la farmacopea antimalárica, estrechamente relacionada a los diferentes conflictos bélicos del último siglo, ha representado un constante desafío y debido a los repetidos problemas de financiación ha resultado claramente inadecuado, especialmente en comparación con el desarrollo de fármacos para otras enfermedades. Como ejemplo cabe destacar que, entre los años 1975-1999, apenas 4 de los cerca de 1400 fármacos registrados en el mundo, eran antimaláricos. Además, la aparición de resistencias por parte del parásito a los fármacos, un problema creciente y global, resulta un grave peligro para el control de esta infección, y representa una presión añadida para los pocos fármacos efectivos todavía disponibles. Con todo, en los últimos años, la malaria se está desprendiendo del status de enfermedad olvidada que arrastraba, e importantes esfuerzos han surgido para el desarrollo e investigación de nuevos fármacos con actividad antimalárica. Basado en el conocimiento adquirido con otras enfermedades infecciosas como la tuberculosis, la organización mundial de la salud promulga actualmente que el tratamiento frente a P. falciparum, la especie responsable de la mayoría de casos graves y la práctica totalidad de las muertes, debe basarse en la terapia combinada, incluyendo a ser posible un derivado de las artemisininas. La elección de los fármacos a combinar debe basarse en la potencial sinergia entre los perfiles farmacocinéticos y terapéuticos de los diferentes componentes, con el objetivo de conseguir una eliminación de la parasitemia rápida, protegiendo al mismo tiempo a los diferentes componentes frente al desarrollo de resistencias.

Objective: The candidate malaria vaccine RTS,S/AS02A is a recombinant protein containing part of the circumsporozoite protein (CSP) sequence of Plasmodium falciparum, linked to the hepatitis B surface antigen and formulated in the proprietary adjuvant system AS02A. In a recent trial conducted in children younger than age five in southern Mozambique, the vaccine demonstrated significant and sustained efficacy against both infection and clinical disease. In a follow-up study to the main trial, breakthrough infections identified in the trial were examined to determine whether the distribution of csp sequences was affected by the vaccine and to measure the multiplicity of infecting parasite genotypes. Design: P. falciparum DNA from isolates collected during the trial was used for genotype studies. Setting: The main trial was carried out in the Manhiça district, Maputo province, Mozambique, between April 2003 and May 2004. Participants: Children from the two cohorts of the main trial provided parasite isolates as follows: children from Cohort 1 who were admitted to hospital with clinical malaria; children from Cohort 1 who were parasite-positive in a cross-sectional survey at study month 8.5; children from Cohort 2 identified as parasite-positive during follow-up by active detection of infection. Outcome: Divergence of DNA sequence encoding the CSP T cell–epitope region sequence from that of the vaccine sequence was measured in 521 isolates. The number of distinct P. falciparum genotypes was also determined. Results: We found no evidence that parasite genotypes from children in the RTS,S/AS02A arm were more divergent than those receiving control vaccines. For Cohort 1 (survey at study month 8.5) and Cohort 2, infections in the vaccine group contained significantly fewer genotypes than those in the control group, (p = 0.035, p = 0.006), respectively, for the two cohorts. This was not the case for children in Cohort 1 who were admitted to hospital (p = 0.478). Conclusions: RTS,S/AS02A did not select for genotypes encoding divergent T cell epitopes in the C-terminal region of CSP in this trial. In both cohorts, there was a modest reduction in the mean number of parasite genotypes harboured by vaccinated children compared with controls, but only among those with asymptomatic infections., Editorial Commentary Background: A recent trial in young children in Mozambique found that an experimental malaria vaccine, RTS,S/AS02A, reduces the risk of clinical malaria, delays time to new infection, and reduces episodes of severe malaria over 18 months. RTS,S/AS02A is based on a particular protein, the circumsporozoite protein, which is expressed on the surface of the malaria parasite at a stage in its life cycle prior to the disease-causing blood-stage infection. Because there are different variants of the circumsporozoite protein in the parasite population, the researchers were concerned that the strain-specific protection offered by RTS,S/AS02A might select for parasites with particular variants of the circumsporozoite gene. They did a follow-up study to investigate this concern, looking to see whether vaccinated children who became infected with malaria had variant forms of the parasite. What this trial shows: The investigators found that there was no increase in how different the variants were from the vaccine-type allele between vaccinated and control individuals. There was a small decrease in the average number of parasite “strains” in vaccinated children compared with controls. However, in children within the trial who were admitted to hospital with clinical malaria, the number of different “strains” of the parasite was no different between vaccinated children and controls. Strengths and limitations: The study asks an important molecular question about whether vaccination with RTS,S/AS02A selects for different variants, specifically escape mutants of the malaria parasite. If the researchers had found such selection, this would suggest that the vaccine's success could be compromised once widely deployed. A limitation of this follow-up study is that it is difficult to interpret these findings because the mode of action of the vaccine is not yet fully understood. It is also difficult to understand how the results might apply to non-hospitalised patients with clinical malaria, because the malarial patients included in this study were exclusively identified through hospital admissions. Contribution to the evidence: This study adds molecular information to the previously reported results on the clinical effectiveness of the RTS,S/AS02A vaccine. The researchers found no evidence that the RTS,S/AS02A vaccine selected for different variants of the malaria parasite.

Background The pre-erythrocytic malaria vaccine RTS,S/AS02A has shown to confer protection against clinical malaria for at least 21 months in a trial in Mozambican children. Efficacy varied between different endpoints, such as parasitaemia or clinical malaria; however the underlying mechanisms that determine efficacy and its duration remain unknown. We performed a new, exploratory analysis to explore differences in the duration of protection among participants to better understand the protection afforded by RTS,S. Methodology/Principal Findings The study was a Phase IIb double-blind, randomized controlled trial in 2022 children aged 1 to 4 years. The trial was designed with two cohorts to estimate vaccine efficacy against two different endpoints: clinical malaria (cohort 1) and infection (cohort 2). Participants were randomly allocated to receive three doses of RTS,S/AS02A or control vaccines. We did a retrospective, unplanned sub-analysis of cohort 2 data using information collected for safety through the health facility-based passive case detection system. Vaccine efficacy against clinical malaria was estimated over the first six-month surveillance period (double-blind phase) and over the following 12 months (single-blind phase), and analysis was per-protocol. Adjusted vaccine efficacy against first clinical malaria episodes in cohort 2 was of 35.4% (95% CI 4.5–56.3; p = 0.029) over the double-blind phase and of 9.0% (−30.6–36.6; p = 0.609) during the single-blind phase. Conclusions/Significance Contrary to observations in cohort 1, where efficacy against clinical malaria did not wane over time, in cohort 2 the efficacy decreases with time. We hypothesize that this reduced duration of protection is a result of the early diagnosis and treatment of infections in cohort 2 participants, preventing sufficient exposure to asexual-stage antigens. On the other hand, the long-term protection against clinical disease observed in cohort 1 may be a consequence of a prolonged exposure to low-dose blood-stage asexual parasitaemia. Trial Registration ClinicalTrials.gov NCT00197041

Objective: The candidate malaria vaccine RTS,S/AS02A is a recombinant protein containing part of the circumsporozoite protein (CSP) sequence of Plasmodium falciparum, linked to the hepatitis B surface antigen and formulated in the proprietary adjuvant system AS02A. In a recent trial conducted in children younger than age five in southern Mozambique, the vaccine demonstrated significant and sustained efficacy against both infection and clinical disease. In a follow-up study to the main trial, breakthrough infections identified in the trial were examined to determine whether the distribution of csp sequences was affected by the vaccine and to measure the multiplicity of infecting parasite genotypes. Design: P. falciparum DNA from isolates collected during the trial was used for genotype studies. Setting: The main trial was carried out in the Manhiça district, Maputo province, Mozambique, between April 2003 and May 2004. Participants: Children from the two cohorts of the main trial provided parasite isolates as follows: children from Cohort 1 who were admitted to hospital with clinical malaria; children from Cohort 1 who were parasite-positive in a cross-sectional survey at study month 8.5; children from Cohort 2 identified as parasite-positive during follow-up by active detection of infection. Outcome: Divergence of DNA sequence encoding the CSP T cell-epitope region sequence from that of the vaccine sequence was measured in 521 isolates. The number of distinct P. falciparum genotypes was also determined. Results: We found no evidence that parasite genotypes from children in the RTS,S/AS02A arm were more divergent than those receiving control vaccines. For Cohort 1 (survey at study month 8.5) and Cohort 2, infections in the vaccine group contained significantly fewer genotypes than those in the control group, (p 1/4 0.035, p 1/4 0.006), respectively, for the two cohorts. This was not the case for children in Cohort 1 who were admitted to hospital (p 1/4 0.478). Conclusions: RTS,S/AS02A did not select for genotypes encoding divergent T cell epitopes in the C-terminal region of CSP in this trial. In both cohorts, there was a modest reduction in the mean number of parasite genotypes harboured by vaccinated children compared with controls, but only among those with asymptomatic infections.

The global need for new antimalarial drugs and new combinations is enormous and urgent,1, 2 but their successful delivery needs resilience to overcome the barriers imposed by expensive and lengthy clinical development plans. Attention is often directed to areas such as southeast Asia, where some antimalarial combinations are failing but transmission intensities are much lower than in sub-Saharan African countries. Children in Africa have frequent and life-threatening malaria infections as they grow up, and these need to be treated safely.

The circulation of poor-quality medicines continues to undermine the fight against many life-threatening diseases. Anti-malarial medicines appear to have been particularly compromised and present a major public health threat in malaria-endemic countries, negatively affecting individuals and their communities. Concerted collaborative efforts are required from global, regional and national organizations, involving the public and private sectors, to address the problem. While many initiatives are underway, a number of unmet needs deserve urgent and increased multisector attention. At the global level, there is a need for an international public health legal framework or treaty on poor-quality medicines, with statutes suitable for integration into national laws. In addition, increased international efforts are required to strengthen the governance of global supply chains and enhance cooperation between national medicine regulation authorities and law enforcement bodies. Increased investment is needed in innovative technologies that will enable healthcare teams to detect poor-quality medicines at all levels of the supply chain. At the regional level, a number of initiatives would be beneficial-key areas are standardization, simplification, and reciprocal recognition of registration processes and development of quality control capacity in regional centres of excellence that are better aligned with public health needs; improved surveillance methods and creation of a framework for compulsory and transparent reporting of poor-quality medicines; additional support for national medicine regulation authorities and other national partner authorities; and an increase in support for regional laboratories to boost their capabilities in detecting poor-quality medicines. It is vital that all stakeholders involved in efforts against poor-quality anti-malarial medicines extend and strengthen their actions in these critical areas and thus effectively support global health development and malaria elimination programmes.