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Journal articleGhani AC, Walker PG, 2015,
Provision of malaria treatment for Ebola case contacts.
, Lancet Infectious Diseases, Vol: 16, Pages: 391-392, ISSN: 1473-3099 -
Journal articleSlater HC, Ross A, Ouedraogo AL, et al., 2015,
Assessing the impact of next-generation rapid diagnostic tests on Plasmodium falciparum malaria elimination strategies
, Nature, Vol: 528, Pages: S94-S101, ISSN: 0028-0836Mass-screen-and-treat and targeted mass-drug-administration strategies are being considered as a means to interrupt transmission of Plasmodium falciparum malaria. However, the effectiveness of such strategies will depend on the extent to which current and future diagnostics are able to detect those individuals who are infectious to mosquitoes. We estimate the relationship between parasite density and onward infectivity using sensitive quantitative parasite diagnostics and mosquito feeding assays from Burkina Faso. We find that a diagnostic with a lower detection limit of 200 parasites per microlitre would detect 55% of the infectious reservoir (the combined infectivity to mosquitoes of the whole population weighted by how often each individual is bitten) whereas a test with a limit of 20 parasites per microlitre would detect 83% and 2 parasites per microlitre would detect 95% of the infectious reservoir. Using mathematical models, we show that increasing the diagnostic sensitivity from 200 parasites per microlitre (equivalent to microscopy or current rapid diagnostic tests) to 2 parasites per microlitre would increase the number of regions where transmission could be interrupted with a mass-screen-and-treat programme from an entomological inoculation rate below 1 to one of up to 4. The higher sensitivity diagnostic could reduce the number of treatment rounds required to interrupt transmission in areas of lower prevalence. We predict that mass-screen-and-treat with a highly sensitive diagnostic is less effective than mass drug administration owing to the prophylactic protection provided to uninfected individuals by the latter approach. In low-transmission settings such as those in Southeast Asia, we find that a diagnostic tool with a sensitivity of 20 parasites per microlitre may be sufficient for targeted mass drug administration because this diagnostic is predicted to identify a similar village population prevalence compared with that currently detected using polym
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Journal articleWu L, van den Hoogen LL, Slater H, et al., 2015,
Comparison of diagnostics for the detection of asymptomatic Plasmodium falciparum infections to inform control and elimination strategies
, Nature, Vol: 528, Pages: S86-S93, ISSN: 0028-0836The global burden of malaria has been substantially reduced over the past two decades. Future efforts to reduce malaria further will require moving beyond the treatment of clinical infections to targeting malaria transmission more broadly in the community. As such, the accurate identification of asymptomatic human infections, which can sustain a large proportion of transmission, is becoming a vital component of control and elimination programmes. We determined the relationship across common diagnostics used to measure malaria prevalence — polymerase chain reaction (PCR), rapid diagnostic test and microscopy — for the detection of Plasmodium falciparum infections in endemic populations based on a pooled analysis of cross-sectional data. We included data from more than 170,000 individuals comparing the detection by rapid diagnostic test and microscopy, and 30,000 for detection by rapid diagnostic test and PCR. The analysis showed that, on average, rapid diagnostic tests detected 41% (95% confidence interval = 26–66%) of PCR-positive infections. Data for the comparison of rapid diagnostic test to PCR detection at high transmission intensity and in adults were sparse. Prevalence measured by rapid diagnostic test and microscopy was comparable, although rapid diagnostic test detected slightly more infections than microscopy. On average, microscopy captured 87% (95% confidence interval = 74–102%) of rapid diagnostic test-positive infections. The extent to which higher rapid diagnostic test detection reflects increased sensitivity, lack of specificity or both, is unclear. Once the contribution of asymptomatic individuals to the infectious reservoir is better defined, future analyses should ideally establish optimal detection limits of new diagnostics for use in control and elimination strategies.
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Journal articlePenny MA, Verity RV, Bever C, et al., 2015,
Public health impact and cost-effectiveness of the RTS,S/AS01 malaria vaccine: a systematic comparison of predictions from four mathematical models
, The Lancet, Vol: 387, Pages: 367-375, ISSN: 0140-6736BackgroundThe 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.MethodsWe 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.FindingsIn 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 18–2
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Journal articleWhite MT, Verity R, Churcher TS, et al., 2015,
Vaccine approaches to malaria control and elimination: Insights from mathematical models
, Vaccine, Vol: 33, Pages: 7544-7550, ISSN: 1873-2518A licensed malaria vaccine would provide a valuable new tool for malaria control and elimination efforts.Several candidate vaccines targeting different stages ofthe malaria parasite’s lifecycle are currently underdevelopment, with one candidate, RTS,S/AS01 for the prevention of Plasmodium falciparum infection,having recently completed Phase III trials. Predicting the public health impact of a candidate malariavaccine requires using clinical trial data to estimate the vaccine’s efficacy profile—the initial efficacyfollowing vaccination and the pattern of waning of efficacy over time. With an estimated vaccine efficacyprofile, the effects of vaccination on malaria transmission can be simulated with the aid of mathematicalmodels.Here, we provide an overview of methods for estimating the vaccine efficacy profiles of pre-erythrocyticvaccines and transmission-blocking vaccines from clinicaltrial data. In the case of RTS,S/AS01, model estimatesfrom Phase II clinical trial data indicate a bi-phasic exponential profile of efficacy against infection,with efficacy waning rapidly in the first 6 months after vaccination followed by a slower rate of waningover the next 4 years. Transmission-blocking vaccines have yet to be tested in large-scale Phase II orPhase III clinical trials so we review ongoing work investigating how a clinical trial might be designed toensure that vaccine efficacy can be estimated with sufficient statistical power. Finally, we demonstratehow parameters estimated from clinical trials can be used to predict the impact of vaccination campaignson malaria using a mathematical model of malaria transmission
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Journal articleWhite MT, Verity R, Griffin JT, et al., 2015,
Immunogenicity of the RTS,S/AS01 malaria vaccine and implications for duration of vaccine efficacy: secondary analysis of data from a phase 3 randomised controlled trial
, Lancet Infectious Diseases, Vol: 15, Pages: 1450-1458, ISSN: 1473-3099BackgroundThe 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.MethodsUsing 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.FindingsRTS,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 effi
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Journal articleCairns ME, Walker PGT, Okell LC, et al., 2015,
Seasonality in malaria transmission: implications for case-management with long-acting artemisinin combination therapy in sub-Saharan Africa
, Malaria Journal, Vol: 14, ISSN: 1475-2875Background: Long-acting artemisinin-based combination therapy (LACT) offers the potential to prevent recurrentmalaria attacks in highly exposed children. However, it is not clear where this advantage will be most important, anddeployment of these drugs is not rationalized on this basis.Methods: To understand where post-treatment prophylaxis would be most beneficial, the relationship betweenseasonality, transmission intensity and the interval between malaria episodes was explored using data from six cohortstudies in West Africa and an individual-based malaria transmission model. The total number of recurrent malariacases per 1000 child-years at risk, and the fraction of the total annual burden that this represents were estimated forsub-Saharan Africa.Results: In settings where prevalence is less than 10 %, repeat malaria episodes constitute a small fraction of thetotal burden, and few repeat episodes occur within the window of protection provided by currently available drugs.However, in higher transmission settings, and particularly in high transmission settings with highly seasonal transmis‑sion, repeat malaria becomes increasingly important, with up to 20 % of the total clinical burden in children estimatedto be due to repeat episodes within 4 weeks of a prior attack.Conclusion: At a given level of transmission intensity and annual incidence, the concentration of repeat malariaepisodes in time, and consequently the protection from LACT is highest in the most seasonal areas. As a result, thedegree of seasonality, in addition to the overall intensity of transmission, should be considered by policy makers whendeciding between ACT that differ in their duration of post-treatment prophylaxis.
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Journal articleWalker PGT, White MT, Griffin JT, et al., 2015,
Malaria morbidity and mortality in Ebola-affected countries caused by decreased health-care capacity, and the potential effect of mitigation strategies: a modelling analysis
, Lancet Infectious Diseases, Vol: 15, Pages: 825-832, ISSN: 1473-3099BackgroundThe ongoing Ebola epidemic in parts of west Africa largely overwhelmed health-care systems in 2014, making adequate care for malaria impossible and threatening the gains in malaria control achieved over the past decade. We quantified this additional indirect burden of Ebola virus disease.MethodsWe estimated the number of cases and deaths from malaria in Guinea, Liberia, and Sierra Leone from Demographic and Health Surveys data for malaria prevalence and coverage of malaria interventions before the Ebola outbreak. We then removed the effect of treatment and hospital care to estimate additional cases and deaths from malaria caused by reduced health-care capacity and potential disruption of delivery of insecticide-treated bednets. We modelled the potential effect of emergency mass drug administration in affected areas on malaria cases and health-care demand.FindingsIf malaria care ceased as a result of the Ebola epidemic, untreated cases of malaria would have increased by 45% (95% credible interval 43–49) in Guinea, 88% (83–93) in Sierra Leone, and 140% (135–147) in Liberia in 2014. This increase is equivalent to 3·5 million (95% credible interval 2·6 million to 4·9 million) additional untreated cases, with 10 900 (5700–21 400) additional malaria-attributable deaths. Mass drug administration and distribution of insecticide-treated bednets timed to coincide with the 2015 malaria transmission season could largely mitigate the effect of Ebola virus disease on malaria.InterpretationThese findings suggest that untreated malaria cases as a result of reduced health-care capacity probably contributed substantially to the morbidity caused by the Ebola crisis. Mass drug administration can be an effective means to mitigate this burden and reduce the number of non-Ebola fever cases within health systems.
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Journal articleGriffin JT, Hollingsworth TD, Reyburn H, et al., 2015,
Gradual acquisition of immunity to severe malaria with increasing exposure
, Proceedings of the Royal Society B: Biological Sciences, Vol: 282, ISSN: 0962-8452 -
Journal articleUpton LM, Brock PM, Churcher TS, et al., 2015,
Lead Clinical and Preclinical Antimalarial Drugs Can Significantly Reduce Sporozoite Transmission to Vertebrate Populations
, ANTIMICROBIAL AGENTS AND CHEMOTHERAPY, Vol: 59, Pages: 490-497, ISSN: 0066-4804- Author Web Link
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- Citations: 19
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Journal articleSlater HC, Walker PGT, Bousema T, et al., 2014,
The Potential Impact of Adding Ivermectin to a Mass Treatment Intervention to Reduce Malaria Transmission: A Modelling Study
, JOURNAL OF INFECTIOUS DISEASES, Vol: 210, Pages: 1972-1980, ISSN: 0022-1899- Author Web Link
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- Citations: 71
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Journal articleBousema T, Okell L, Felger I, et al., 2014,
Asymptomatic malaria infections: detectability, transmissibility and public health relevance
, NATURE REVIEWS MICROBIOLOGY, Vol: 12, Pages: 833-840, ISSN: 1740-1526- Cite
- Citations: 479
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Journal articleWhite MT, Karl S, Battle K, et al., 2014,
Modelling the contribution of the hypnozoite reservoir to Plasmodium vivax transmission
, eLife, Vol: 3, ISSN: 2050-084XPlasmodium vivax relapse infections occur following activation of latent liver-stagesparasites (hypnozoites) causing new blood-stage infections weeks to months after the initialinfection. We develop a within-host mathematical model of liver-stage hypnozoites, and validateit against data from tropical strains of P. vivax. The within-host model is embedded in a P. vivaxtransmission model to demonstrate the build-up of the hypnozoite reservoir following newinfections and its depletion through hypnozoite activation and death. The hypnozoite reservoiris predicted to be over-dispersed with many individuals having few or no hypnozoites, and somehaving intensely infected livers. Individuals with more hypnozoites are predicted to experiencemore relapses and contribute more to onwards P. vivax transmission. Incorporating hypnozoitekilling drugs such as primaquine into first-line treatment regimens is predicted to cause substantialreductions in P. vivax transmission as individuals with the most hypnozoites are more likely torelapse and be targeted for treatment.
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Journal articleOkell LC, Cairns M, Griffin JT, et al., 2014,
Contrasting benefits of different artemisinin combination therapies as first-line malaria treatments using model-based cost-effectiveness analysis
, Nature Communications, Vol: 5, ISSN: 2041-1723There are currently several recommended drug regimens for uncomplicated falciparummalaria in Africa. Each has different properties that determine its impact on diseaseburden. Two major antimalarial policy options are artemether–lumefantrine (AL) anddihydroartemisinin–piperaquine (DHA–PQP). Clinical trial data show that DHA–PQP provideslonger protection against reinfection, while AL is better at reducing patient infectiousness.Here we incorporate pharmacokinetic-pharmacodynamic factors, transmission-reducingeffects and cost into a mathematical model and simulate malaria transmission and treatmentin Africa, using geographically explicit data on transmission intensity and seasonality,population density, treatment access and outpatient costs. DHA–PQP has a modestly higherestimated impact than AL in 64% of the population at risk. Given current higher costestimates for DHA–PQP, there is a slightly greater cost per case averted, except in areas withhigh, seasonally varying transmission where the impact is particularly large. We find that alocally optimized treatment policy can be highly cost effective for reducing clinical malariaburden.
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Journal articleWhite MT, Griffin JT, Akpogheneta O, et al., 2014,
Dynamics of the Antibody Response to <i>Plasmodium falciparum</i> Infection in African Children
, JOURNAL OF INFECTIOUS DISEASES, Vol: 210, Pages: 1115-1122, ISSN: 0022-1899- Author Web Link
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- Citations: 91
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