Decision-making on malaria vaccine introduction: the role of cost-effectiveness analyses

Insights from modelling malaria vaccines for policy decisions: the focus on RTS,S

Mathematical models are increasingly used to inform decisions throughout product development pathways from pre-clinical studies to country implementation of novel health interventions. This review illustrates the utility of simulation approaches by reviewing the literature on malaria vaccine modelling, with a focus on its link to the development of policy guidance for the first licensed product, RTS,S/AS01. The main contributions of modelling studies have been in inferring the mechanism of action and efficacy profile of RTS,S; to predicting the public health impact; and economic modelling mainly comprising cost-effectiveness analysis. The value of both product-specific and generic modelling of vaccines is highlighted.

Endectocides as a complementary intervention in the malaria control program: a systematic review

BACKGROUND

Malaria is the most common vector-borne disease transmitted to humans by Anopheles mosquitoes. Endectocides and especially ivermectin will be available as a vector control tool soon. The current review could be valuable for trial design and clinical studies to control malaria transmission.

METHODS

PubMed/MEDLINE, Scopus, Web of Science, and Science Direct were searched for original English published papers on ("Malaria chemical control" OR "Malaria elimination" OR "Anopheles vector control" OR "Malaria zooprophylaxis") AND ("Systemic insecticides" OR "Endectocides" OR "Ivermectin"). The last search was from 19 June 2019 to 31 December 2019. It was updated on 17 November 2020. Two reviewers (SG and FGK) independently reviewed abstracts and full-text articles. Data were extracted by one person and checked by another. As meta-analyses were not possible, a qualitative summary of results was performed.

RESULTS

Thirty-six published papers have used systemic insecticides/endectocides for mosquito control. Most of the studies (56.75%) were done on Anopheles gambiae complex species on doses from 150 μg/kg to 400 μg/kg in several studies. Target hosts for employing systemic insecticides/drugs were animals (44.2%, including rabbit, cattle, pig, and livestock) and humans (32.35%).

CONCLUSIONS

Laboratory and field studies have highlighted the potential of endectocides in malaria control. Ivermectin and other endectocides could soon serve as novel malaria transmission control tools by reducing the longevity of Anopheles mosquitoes that feed on treated hosts, potentially decreasing Plasmodium parasite transmission when used as mass drug administration (MDA).

Environmental modifiers of RTS,S/AS01 malaria vaccine efficacy in Lilongwe, Malawi

BACKGROUND

RTS,S/AS01 is the first vaccine against malaria to undergo pilot implementation, beginning in 2019 and vaccinating 360,000 children per year in Malawi, Ghana, and Kenya. The four-dose vaccine is given as a primary three-dose series with a fourth dose given approximately 18 months later. The efficacy of RTS,S/AS01 was variable among the 11 sites participating in the 2009-2014 phase III trial (MALARIA-055, NCT00866619), possibly due to differences in transmission intensity. However, a within-site examination of environmental factors related to transmission intensity and their impact on vaccine efficacy has yet to be conducted.

METHODS

We implemented the phase III RTS,S/AS01 trial at the Malawi site, which enrolled 1578 infants (6-12 weeks) and children (5-17 months) living in the Lilongwe District in Central Malawi and followed them for 3 years between 2009 and 2014. A global positioning system survey and an ecological questionnaire were conducted to collect participant household locations and characteristics, while additional data on background malaria prevalence were obtained from a concurrent Malaria Transmission Intensity (MTI) survey. Negative binomial regression models were used to assess whether the efficacy of the vaccine varied by estimated background malaria prevalence, household roof type, or amount of nearby vegetation.

RESULTS

Vaccine efficacy did not significantly vary by estimated malaria prevalence or by roof type. However, increased vegetation cover was associated with an increase in the efficacy of the three-dose primary RTS,S/AS01 series in the 18 months before the fourth dose and a decrease in the efficacy of the primary vaccine series in the second 18 months following, if the fourth dose was not given. Vegetation cover did not alter the efficacy of the fourth dose in a statistically or practically significant manner.

CONCLUSIONS

Vegetation coverage in this study site might be a proxy for nearness to rivers or branching, shallow wetlands called "dambos" which could serve as breeding sites for mosquitoes. We observed statistically significant modification of the efficacy of RTS,S/AS01 by forest cover, suggesting that initial vaccine efficacy and the importance of the fourth dose varies based on ecological context.

TRIAL REGISTRATION

Efficacy of GSK Biologicals' Candidate Malaria Vaccine (257049) Against Malaria Disease Caused by P. falciparum Infection in Infants and Children in Africa. NCT00866619 prospectively registered 20 March 2009.

Effect of immune regulatory pathways after immunization with GMZ2 malaria vaccine candidate in healthy lifelong malaria-exposed adults

BACKGROUND

Despite appreciable immunogenicity in malaria-naive populations, many candidate malaria vaccines are considerably less immunogenic in malaria-exposed populations. This could reflect induction of immune regulatory mechanisms involving Human Leukocyte Antigen G (HLA-G), regulatory T (Treg), and regulatory B (Breg) cells. Here, we addressed the question whether there is correlation between these immune regulatory pathways and both plasmablast frequencies and vaccine-specific IgG concentrations.

METHODS

Fifty Gabonese adults with lifelong exposure to Plasmodium spp were randomized to receive three doses of either 30 µg or 100 µg GMZ2-CAF01, or 100 µg GMZ2-alum, or control vaccine (rabies vaccine) at 4-week intervals. Only plasma and peripheral blood mononuclear cells isolated from blood samples collected before (D0) and 28 days after the third vaccination (D84) of 35 participants were used to measure sHLA-G levels and anti-GMZ2 IgG concentrations, and to quantify Treg, Breg and plasmablast cells. Vaccine efficacy was assessed using controlled human malaria infection (CHMI) by direct venous inoculation of Plasmodium falciparum sporozoites (PfSPZ Challenge).

RESULTS

The sHLA-G concentration increased from D0 to D84 in all GMZ2 vaccinated participants and in the control group, whereas Treg frequencies increased only in those receiving 30 µg or 100 µg GMZ2-CAF01. The sHLA-G level on D84 was associated with a decrease of the anti-GMZ2 IgG concentration, whereas Treg frequencies on D0 or on D84, and Breg frequency on D84 were associated with lower plasmablast frequencies. Importantly, having a D84:D0 ratio of sHLA-G above the median was associated with an increased risk of P. falciparum infection after sporozoites injection.

CONCLUSION

Regulatory immune responses are induced following immunization. Stronger sHLA-G and Treg immune responses may suppress vaccine induced immune responses, and the magnitude of the sHLA-G response increased the risk of Plasmodium falciparum infection after CHMI. These findings could have implications for the design and testing of malaria vaccine candidates in semi-immune individuals.

Case reduction and cost-effectiveness of the RTS,S/AS01 malaria vaccine alongside bed nets in Lilongwe, Malawi

BACKGROUND

RTS,S/AS01, the most advanced vaccine against malaria, is now undergoing pilot implementation in Malawi, Ghana, and Kenya where an estimated 360,000 children will be vaccinated each year. In this study we evaluate RTS,S/AS01 alongside bed net use and estimate cost-effectiveness.

METHODS

RTS,S/AS01 phase III trial and bed net prevalence data were used to determine the effect of vaccination in the urban/periurban and rural areas of Lilongwe, Malawi. Cost data were used to calculate the cost-effectiveness of various interventions over three years.

FINDINGS

Since bed nets reduce malaria incidence and homogeneous vaccine efficacy was assumed, participants without bed nets received greater relative benefit from vaccination with RTS,S/AS01 than participants with bed nets. Similarly, since malaria incidence in rural Lilongwe is higher than in urban Lilongwe, the impact and cost-effectiveness of vaccine interventions is increased in rural areas. In rural Lilongwe, we estimated that vaccinating one child without a bed net would prevent 2·59 (1·62 to 3·38) cases of malaria over three years, corresponding to a cost of $10·08 (7·71 to 16·13) per case averted. Alternatively, vaccinating one child with a bed net would prevent 1·59 (0·87 to 2·57) cases, corresponding to $16·43 (10·16 to 30·06) per case averted. Providing RTS,S/AS01 to 30,000 children in rural Lilongwe was estimated to cost $782,400 and to prevent 58,611 (35,778 to 82,932) cases of malaria over a three-year period. Joint interventions providing both vaccination and bed nets (to those without them) were estimated to prevent additional cases of malaria and to be similarly cost-effective, compared to vaccine-only interventions.

INTERPRETATION

To maximize malaria prevention, vaccination and bed net distribution programs could be integrated.

FUNDING

Impacts of Environment, Host Genetics and Antigen Diversity on Malaria Vaccine Efficacy (1R01AI137410-01).

Single dose treatment of malaria - current status and perspectives

INTRODUCTION

Despite increased international efforts for control and ultimate elimination, malaria remains a major health problem. Currently, artemisinin-based combination therapies are the treatment of choice for uncomplicated malaria exhibiting high efficacy in clinical trial settings in sub-Saharan Africa. However, their administration over a three-day period is associated with important problems of treatment adherence resulting in markedly reduced effectiveness of currently recommended antimalarials under real world settings.

AREAS COVERED

Antimalarial drug candidates and antimalarial drug combinations currently under advanced clinical development for the indication as single dose antimalarial therapy. Expert commentary: Several new drug candidates and combinations are currently undergoing pivotal proof-of-concept studies or clinical development programmes. The development of a single dose combination therapy would constitute a breakthrough in the control of malaria. Such an innovative treatment approach would simultaneously close the effectiveness gap of current three-day therapies and revolutionize population based interventions in the context of malaria elimination campaigns.

Cost-effectiveness analysis of rapid diagnostic tests for G6PD deficiency in patients with Plasmodium vivax malaria in the Brazilian Amazon

BACKGROUND

The use of primaquine (PQ) for radical treatment of Plasmodium vivax in carriers of G6PD deficiency (G6PDd) constitutes the main factor associated with severe haemolysis in G6PDd. The current study aimed to estimate the incremental cost-effectiveness ratio of using a rapid diagnostic test (RDT) to detect G6PDd in male patients with P. vivax malaria in the Brazilian Amazon, in comparison with the routine indicated by the Programme for Malaria Control, which does not include this evaluation.

METHODS

A cost-effectiveness analysis of estimated RDT use was carried out for the Brazilian Amazon for the year 2013, considering the perspective of the Brazilian Public Health System. Using decision trees, estimates were compared for two different RDT strategies for G6PDd in male individuals infected with P. vivax before being prescribed PQ, with the routine indicated in Brazil, which does not include prior diagnosis of G6PDd. The first strategy considered the combined use of RDT BinaxNOW(®) G6PD (BX-G6PD) in municipalities with more than 100,000 inhabitants and the routine programme (RP) for the other municipalities. Operational limitations related to the required temperature control and venous blood collection currently restrict the use of RDT BX-G6PD in small municipalities. The second strategy considered the use of the RDT CareStart™ G6PD (CS-G6PD) in 100 % of the municipalities. The analysis was carried out for the outcomes: "adequately diagnosed case" and "hospitalization avoided".

RESULTS

For the outcome "adequately diagnosed case", comparing the RDT strategies based on RDT with the routine control programme (RP), the CS-G6PD strategy was the most cost-effective, with BX-G6PD extendedly dominating (the ICER of BX-G6PD compared with RP was higher than the ICER of CS-G6PD compared with RP). CS-G6PD dominated the other strategies for the "hospitalization avoided" outcome.

CONCLUSION

The CS-G6PD strategy is cost-effective for adequately diagnosing cases and avoiding hospitalization. This information can help in decision-making, both in incorporating prior diagnosis in the use of PQ and to promote greater safety among G6PD deficient individuals in the Brazilian Amazon P. vivax endemic areas.

Public health impact and cost-effectiveness of the RTS,S/AS01 malaria vaccine: a systematic comparison of predictions from four mathematical models

BACKGROUND

The phase 3 trial of the RTS,S/AS01 malaria vaccine candidate showed modest efficacy of the vaccine against Plasmodium falciparum malaria, but was not powered to assess mortality endpoints. Impact projections and cost-effectiveness estimates for longer timeframes than the trial follow-up and across a range of settings are needed to inform policy recommendations. We aimed to assess the public health impact and cost-effectiveness of routine use of the RTS,S/AS01 vaccine in African settings.

METHODS

We compared four malaria transmission models and their predictions to assess vaccine cost-effectiveness and impact. We used trial data for follow-up of 32 months or longer to parameterise vaccine protection in the group aged 5-17 months. Estimates of cases, deaths, and disability-adjusted life-years (DALYs) averted were calculated over a 15 year time horizon for a range of levels of Plasmodium falciparum parasite prevalence in 2-10 year olds (PfPR2-10; range 3-65%). We considered two vaccine schedules: three doses at ages 6, 7·5, and 9 months (three-dose schedule, 90% coverage) and including a fourth dose at age 27 months (four-dose schedule, 72% coverage). We estimated cost-effectiveness in the presence of existing malaria interventions for vaccine prices of US$2-10 per dose.

FINDINGS

In regions with a PfPR2-10 of 10-65%, RTS,S/AS01 is predicted to avert a median of 93,940 (range 20,490-126,540) clinical cases and 394 (127-708) deaths for the three-dose schedule, or 116,480 (31,450-160,410) clinical cases and 484 (189-859) deaths for the four-dose schedule, per 100,000 fully vaccinated children. A positive impact is also predicted at a PfPR2-10 of 5-10%, but there is little impact at a prevalence of lower than 3%. At $5 per dose and a PfPR2-10 of 10-65%, we estimated a median incremental cost-effectiveness ratio compared with current interventions of $30 (range 18-211) per clinical case averted and $80 (44-279) per DALY averted for the three-dose schedule, and of $25 (16-222) and $87 (48-244), respectively, for the four-dose schedule. Higher ICERs were estimated at low PfPR2-10 levels.

INTERPRETATION

We predict a significant public health impact and high cost-effectiveness of the RTS,S/AS01 vaccine across a wide range of settings. Decisions about implementation will need to consider levels of malaria burden, the cost-effectiveness and coverage of other malaria interventions, health priorities, financing, and the capacity of the health system to deliver the vaccine.

FUNDING

PATH Malaria Vaccine Initiative; Bill & Melinda Gates Foundation; Global Good Fund; Medical Research Council; UK Department for International Development; GAVI, the Vaccine Alliance; WHO.

Costing RTS,S introduction in Burkina Faso, Ghana, Kenya, Senegal, Tanzania, and Uganda: A generalizable approach drawing on publicly available data

Recent results from the phase 3 trial of RTS,S/AS01 malaria vaccine show that the vaccine induced partial protection against clinical malaria in infants and children; given the high burden of the disease it is currently considered for use in malaria endemic countries. To inform adoption decisions the paper proposes a generalizable methodology to estimate the cost of vaccine introduction using routinely collected and publicly available data from the cMYP, UNICEF, and WHO-CHOICE. Costing is carried out around a set of generic activities, assumptions, and inputs for delivery of immunization services adapted to a given country and deployment modality to capture among other factors the structure of the EPI program, distribution model, geography, and demographics particular to the setting. The methodology is applied to estimate the cost of RTS,S introduction in Burkina Faso, Ghana, Kenya, Senegal, Tanzania, and Uganda. At an assumed vaccine price of $5 per dose and given our assumptions on coverage and deployment strategy, we estimate total economic program costs for a 6–9 months cohort within $23.11–$28.28 per fully vaccinated child across the 6 countries. Net of procurement, costs at country level are substantial; for instance in Tanzania these could add as much as $4.2 million per year or an additional $2.4 per infant depending on the level of spare capacity in the system. Differences in cost of vaccine introduction across countries are primarily driven by differences in cost of labour. Overall estimates generated with the methodology result in costs within the ranges reported for other new vaccines introduced in SSA and capture multiple sources of heterogeneity in costs across countries. Further validation with data from field trials will support use of the methodology while also serving as a validation for cMYP and WHO-CHOICE as resources for costing health interventions in the region.

Paths to a malaria vaccine illuminated by parasite genomics

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Discovery of vaccine candidate antigens by parasite genome sequence analyses.

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Genetic crosses, linkage group selection, and functional studies on parasites.

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Characterizing developmental and epigenetic variation alongside allelic polymorphism.

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Selection by naturally acquired immune responses helps to focus vaccine design.

More human death and disease is caused by malaria parasites than by all other eukaryotic pathogens combined. As early as the sequencing of the first human genome, malaria parasite genomics was prioritized to fuel the discovery of vaccine candidate antigens. This stimulated increased research on malaria, generating new understanding of the cellular and molecular mechanisms of infection and immunity. This review of recent developments illustrates how new approaches in parasite genomics, and increasingly large amounts of data from population studies, are helping to identify antigens that are promising lead targets. Although these results have been encouraging, effective discovery and characterization need to be coupled with more innovation and funding to translate findings into newly designed vaccine products for clinical trials.

The role of mathematical modelling in the development of recommendations in the 2013 WHO consolidated antiretroviral therapy guidelines

Despite the exponential growth in the literature on modelling and simulation studies of impact and cost-effectiveness in different aspects of healthcare, there is no clear consensus on the appropriate role of modelling in the development of recommendations in clinical guidelines. This is compounded both by the lack of a standardised approach to assess the quality of modelling, and lack of clarity on its positioning within the GRADE (Grading of Recommendations, Assessment, Development, and Evaluation) method for decision-making in the development of WHO guidelines, that considers both evidence from systematic reviews of randomized clinical trials (RTCs) or observational studies, together with stakeholder values and preferences, resource use, and feasibility issues. In the development of the 2013 WHO Consolidated Guidelines on the use of Antiretroviral drugs for treating and preventing HIV infection, a series of modelling projects were undertaken to inform the recommendations on eligibility criteria for ART initiation, and approaches to monitoring for treatment response. We report our experiences, challenges encountered, and several key considerations to guide the future use of modelling in the development of WHO guidelines. These are: (1) Transparency in the conduct and reporting of model inputs and results; (2) The need for agreed standards for critical appraisal and use of modelling data in healthcare policy making; (3) recognition that modelling of cost-effectiveness is only one component of decision-making in development of WHO recommendations and in priority-setting; (4) The need for closer interaction and an ongoing dialogue between modellers and model end-users or decision-makers; (5) the important role of WHO in convening and facilitating comparative assessment of multiple models; and (6) The need to optimize research and data collection to inform modelling studies.

Modeling the public health impact of malaria vaccines for developers and policymakers

Background

Efforts to develop malaria vaccines show promise. Mathematical model-based estimates of the potential demand, public health impact, and cost and financing requirements can be used to inform investment and adoption decisions by vaccine developers and policymakers on the use of malaria vaccines as complements to existing interventions. However, the complexity of such models may make their outputs inaccessible to non-modeling specialists. This paper describes a Malaria Vaccine Model (MVM) developed to address the specific needs of developers and policymakers, who need to access sophisticated modeling results and to test various scenarios in a user-friendly interface. The model’s functionality is demonstrated through a hypothetical vaccine.

Methods

The MVM has three modules: supply and demand forecast; public health impact; and implementation cost and financing requirements. These modules include pre-entered reference data and also allow for user-defined inputs. The model includes an integrated sensitivity analysis function. Model functionality was demonstrated by estimating the public health impact of a hypothetical pre-erythrocytic malaria vaccine with 85% efficacy against uncomplicated disease and a vaccine efficacy decay rate of four years, based on internationally-established targets. Demand for this hypothetical vaccine was estimated based on historical vaccine implementation rates for routine infant immunization in 40 African countries over a 10-year period. Assumed purchase price was $5 per dose and injection equipment and delivery costs were $0.40 per dose.

Results

The model projects the number of doses needed, uncomplicated and severe cases averted, deaths and disability-adjusted life years (DALYs) averted, and cost to avert each. In the demonstration scenario, based on a projected demand of 532 million doses, the MVM estimated that 150 million uncomplicated cases of malaria and 1.1 million deaths would be averted over 10 years. This is equivalent to 943 uncomplicated cases and 7 deaths averted per 1,000 vaccinees. In discounted 2011 US dollars, this represents $11 per uncomplicated case averted and $1,482 per death averted. If vaccine efficacy were reduced to 75%, the estimated uncomplicated cases and deaths averted over 10 years would decrease by 14% and 19%, respectively.

Conclusions

The MVM can provide valuable information to assist decision-making by vaccine developers and policymakers, information which will be refined and strengthened as field studies progress allowing further validation of modeling assumptions.