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  • Journal article
    Green N, Agossa F, Yovogan B, Oxborough R, Kitau J, Müller P, Constant E, Rowland M, Tchacaya EFS, Benjamin KG, Churcher TS, Betancourt M, Sherrard-Smith Eet al., 2022,

    An evidence synthesis approach for combining different data sources illustrated using entomological efficacy of insecticides for indoor residual spraying

    , PLoS One, Vol: 17, Pages: e0263446-e0263446, ISSN: 1932-6203

    BackgroundProspective malaria public health interventions are initially tested for entomological impact using standardised experimental hut trials. In some cases, data are collated as aggregated counts of potential outcomes from mosquito feeding attempts given the presence of an insecticidal intervention. Comprehensive data i.e. full breakdowns of probable outcomes of mosquito feeding attempts, are more rarely available. Bayesian evidence synthesis is a framework that explicitly combines data sources to enable the joint estimation of parameters and their uncertainties. The aggregated and comprehensive data can be combined using an evidence synthesis approach to enhance our inference about the potential impact of vector control products across different settings over time.MethodsAggregated and comprehensive data from a meta-analysis of the impact of Pirimiphos-methyl, an indoor residual spray (IRS) product active ingredient, used on wall surfaces to kill mosquitoes and reduce malaria transmission, were analysed using a series of statistical models to understand the benefits and limitations of each.ResultsMany more data are available in aggregated format (N = 23 datasets, 4 studies) relative to comprehensive format (N = 2 datasets, 1 study). The evidence synthesis model had the smallest uncertainty at predicting the probability of mosquitoes dying or surviving and blood-feeding. Generating odds ratios from the correlated Bernoulli random sample indicates that when mortality and blood-feeding are positively correlated, as exhibited in our data, the number of successfully fed mosquitoes will be under-estimated. Analysis of either dataset alone is problematic because aggregated data require an assumption of independence and there are few and variable data in the comprehensive format.ConclusionsWe developed an approach to combine sources from trials to maximise the inference that can be made from such data and that is applicable to other systems. Bayesian evidence synthes

  • Journal article
    Sherrard-Smith E, Winskill P, Hamlet A, Ngufor C, N'Guessan R, Guelbeogo MW, Sanou A, Nash RK, Hill A, Russell EL, Woodbridge M, Tungu P, Kont MD, McLean T, Fornadel C, Richardson JH, Donnelly MJ, Staedke SG, Gonahasa S, Protopopoff N, Rowland M, Churcher TSet al., 2022,

    Optimising the deployment of vector control tools against malaria: a data-informed modelling study

    , The Lancet Planetary Health, Vol: 6, Pages: e100-e109, ISSN: 2542-5196

    Background Concern that insecticide resistant mosquitoes are threatening malaria control has driven the development of new types of insecticide treated nets (ITNs) and indoor residual spraying (IRS). Malaria control programmes have a choice of vector control interventions though it is unclear which should be used to combat the disease.MethodsThe entomological impact of ITNs combining a pyrethroid insecticide with the synergist piperonyl butoxide (PBO) is characterised from experimental hut trials and used to parameterise a malaria transmission dynamics model. Model projections are validated for two sites by comparing results to data from pyrethroid-PBO ITN and IRS randomised control trials (RCTs). Models are used to identify optimum intervention packages for scenarios with varying budget, price, entomological and epidemiological factors. Findings Combining entomological data and models can reasonably predict changes in malaria in the Tanzanian and Ugandan RCTs. Models indicate switching from pyrethroid-only to pyrethroid-PBO ITNs could avert up to twice as many cases, though the additional benefit is highly variable and depends upon setting. Annual delivery of long-lasting, non-pyrethroid IRS is projected to prevent substantially more cases over 3-years, but pyrethroid-PBO ITNs tend to be the most cost-effective intervention per case averted. An online tool (MINT) provides users with a method of designing intervention packages given their setting and budget. InterpretationThe most cost-effective vector control package will vary locally. Models able to recreate results of RCTs can be used to extrapolate outcomes elsewhere to support evidence-based decision making for investment in vector control.FundingMedical Research Council, IVCC, Wellcome Trust.

  • Journal article
    Unwin H, Mwandigha L, Winskill P, Ghani A, Hogan Aet al., 2021,

    Analysis of the potential for a malaria vaccine to reduce gaps in malaria intervention coverage

    , Malaria Journal, Vol: 20, Pages: 1-11, ISSN: 1475-2875

    BackgroundThe RTS,S/AS01 malaria vaccine is currently being evaluated in a cluster-randomized pilot implementation programme in three African countries. This study seeks to identify whether vaccination could reach additional children who are at risk from malaria but do not currently have access to, or use, core malaria interventions.MethodsUsing data from household surveys, the overlap between malaria intervention coverage and childhood vaccination (diphtheria-tetanus-pertussis dose 3, DTP3) uptake in 20 African countries with at least one first administrative level unit with Plasmodium falciparum parasite prevalence greater than 10% was calculated. Multilevel logistic regression was used to explore patterns of overlap by demographic and socioeconomic variables. The public health impact of delivering RTS,S/AS01 to those children who do not use an insecticide-treated net (ITN), but who received the DTP3 vaccine, was also estimated.ResultsUptake of DTP3 was higher than malaria intervention coverage in most countries. Overall, 34% of children did not use ITNs and received DTP3, while 35% of children used ITNs and received DTP3, although this breakdown varied by country. It was estimated that there are 33 million children in these 20 countries who do not use an ITN. Of these, 23 million (70%) received the DTP3 vaccine. Vaccinating those 23 million children who receive DTP3 but do not use an ITN could avert up to an estimated 9.7 million (range 8.5–10.8 million) clinical malaria cases each year, assuming all children who receive DTP3 are administered all four RTS,S doses. An additional 10.8 million (9.5–12.0 million) cases could be averted by vaccinating those 24 million children who receive the DTP3 vaccine and use an ITN. Children who had access to or used an ITN were 9–13% more likely to reside in rural areas compared to those who had neither intervention regardless of vaccination status. Mothers’ education status was a strong predictor of inte

  • Conference paper
    Paschalidis A, Watson OJ, Verity RJ, Bailey JAet al., 2021,

    COMPLEXITY OF INFECTION ESTIMATION WITH ALLELE FREQUENCIES

    , Publisher: AMER SOC TROP MED & HYGIENE, Pages: 216-216, ISSN: 0002-9637
  • Journal article
    Nash RK, Lambert B, NGuessan R, Ngufor C, Rowland M, Oxborough R, Moore S, Tungu P, Sherrard-Smith E, Churcher TSet al., 2021,

    Systematic review of the entomological impact of insecticide-treated nets evaluated using experimental hut trials in Africa

    , Current Research in Parasitology & Vector-Borne Diseases, Vol: 1, Pages: 1-13, ISSN: 2667-114X

    Resistance of anopheline mosquitoes to pyrethroid insecticides is spreading rapidly across sub-Saharan Africa, diminishing the efficacy of insecticide-treated nets (ITNs) – the primary tool for preventing malaria. The entomological efficacy of indoor vector control interventions can be measured in experimental hut trials (EHTs), where hut structures resemble local housing, but allow the collection of mosquitoes that entered, exited, blood-fed and/or died. There is a need to understand how the spread of resistance changes ITN efficacy and to elucidate factors influencing EHT results, including differences in experimental hut design, to support the development of novel vector control tools. A comprehensive database of EHTs was compiled following a systematic review to identify all known trials investigating ITNs or indoor residual spraying across sub-Saharan Africa. This analysis focuses on EHTs investigating ITNs and uses Bayesian statistical models to characterise the complex interaction between ITNs and mosquitoes, the between-study variability, and the impact of pyrethroid resistance. As resistance rises, the entomological efficacy of ITNs declines. They induce less mortality and are less likely to deter mosquitoes from entering huts. Despite this, ITNs continue to offer considerable personal protection by reducing mosquito feeding until resistance reaches high levels. There are clear associations between the different entomological impacts of ITNs, though there is still substantial variability between studies, some of which can be accounted for by hut design. The relationship between EHT outcomes and the level of resistance (as measured by discriminating dose bioassays) is highly uncertain. The meta-analyses show that EHTs are an important reproducible assay for capturing the complex entomological efficacy of ITNs on blood-feeding mosquitoes. The impact of pyrethroid resistance on these measures appears broadly consistent across a wide geographical area onc

  • Journal article
    Okell L, Whittaker C, Ghani A, Slater H, Nash R, Bousema T, Drakeley Cet al., 2021,

    Global patterns of submicroscopic Plasmodium falciparum malaria infection: insights from a systematic review and meta-analysis of population surveys

    , The Lancet Microbe, Vol: 2, Pages: e366-e374, ISSN: 2666-5247

    Background: Adoption of molecular techniques to detect Plasmodium falciparum infection has revealed many previously undetected (by microscopy) yet transmissible low-density infections. The proportion of these infections is typically highest in low transmission settings, but drivers of submicroscopic infection remain unclear. Here, we update a previously conducted systematic review of asexual P. falciparum prevalence by microscopy and polymerase chain reaction (PCR) in the same population. We conduct a meta-analysis to explore potential drivers of submicroscopic infection and identify the locations where submicroscopic infections are most common. Methods: PubMed and Web of Science databases were searched up to 11th October 2020 for cross-sectional studies reporting data on asexual P.falciparum prevalence by both microscopy and PCR. Surveys of pregnant women, where participants had been chosen based on symptoms/treatment or that did not involve a population from a defined location were excluded. Both the number of individuals tested and positive by microscopy and PCR for P. falciparum infection were extracted from each reference. Bayesian regression modelling was used to explore determinants of the size of the submicroscopic reservoir including geography, seasonality, age, methodology and current/historical patterns of transmission.Findings: A total of 166 references containing 551 cross-sectional survey microscopy/PCR prevalence pairs were included. Our results highlight that submicroscopic infections predominate in low transmission settings across all settings, but also reveal marked geographical variation, with the proportion of infections that are submicroscopic being highest in South American surveys and lowest in West African studies. Whilst current transmission levels partly explain these results, we find that historical transmission intensity also represents a crucial determinant of the size of the submicroscopic reservoir, as does the demographic structure of

  • Journal article
    Brazeau NF, Mitchell CL, Morgan AP, Deutsch-Feldman M, Watson OJ, Thwai KL, Gelabert P, van Dorp L, Keeler CY, Waltmann A, Emch M, Gartner V, Redelings B, Wray GA, Mwandagalirwa MK, Tshefu AK, Likwela JL, Edwards JK, Verity R, Parr JB, Meshnick SR, Juliano JJet al., 2021,

    The epidemiology of <i>Plasmodium vivax</i> among adults in the Democratic Republic of the Congo

    , NATURE COMMUNICATIONS, Vol: 12
  • Journal article
    Morris AL, Ghani A, Ferguson N, 2021,

    Fine-scale estimation of key life-history parameters of malaria vectors: implications for next-generation vector control technologies

    , Parasites and Vectors, Vol: 14, Pages: 1-12, ISSN: 1756-3305

    BackgroundMosquito control has the potential to significantly reduce malaria burden on a region, but to influence public health policy must also show cost-effectiveness. Gaps in our knowledge of mosquito population dynamics mean that mathematical modelling of vector control interventions have typically made simplifying assumptions about key aspects of mosquito ecology. Often, these assumptions can distort the predicted efficacy of vector control, particularly next-generation tools such as gene drive, which are highly sensitive to local mosquito dynamics.MethodsWe developed a discrete-time stochastic mathematical model of mosquito population dynamics to explore the fine-scale behaviour of egg-laying and larval density dependence on parameter estimation. The model was fitted to longitudinal mosquito population count data using particle Markov chain Monte Carlo methods.ResultsBy modelling fine-scale behaviour of egg-laying under varying density dependence scenarios we refine our life history parameter estimates, and in particular we see how model assumptions affect population growth rate (Rm), a crucial determinate of vector control efficacy.ConclusionsSubsequent application of these new parameter estimates to gene drive models show how the understanding and implementation of fine-scale processes, when deriving parameter estimates, may have a profound influence on successful vector control. The consequences of this may be of crucial interest when devising future public health policy.

  • Journal article
    Hogan AB, Winskill P, Watson OJ, Walker PGT, Whittaker C, Baguelin M, Brazeau NF, Charles GD, Gaythorpe KAM, Hamlet A, Knock E, Laydon DJ, Lees JA, Løchen A, Verity R, Whittles LK, Muhib F, Hauck K, Ferguson NM, Ghani ACet al., 2021,

    Within-country age-based prioritisation, global allocation, and public health impact of a vaccine against SARS-CoV-2: a mathematical modelling analysis

    , Vaccine, Vol: 39, Pages: 2995-3006, ISSN: 0264-410X

    The worldwide endeavour to develop safe and effective COVID-19 vaccines has been extraordinary, and vaccination is now underway in many countries. However, the doses available in 2021 are likely to be limited. We extended a mathematical model of SARS-CoV-2 transmission across different country settings to evaluate the public health impact of potential vaccines using WHO-developed target product profiles. We identified optimal vaccine allocation strategies within- and between-countries to maximise averted deaths under constraints on dose supply. We found that the health impact of SARS-CoV-2 vaccination depends on the cumulative population-level infection incidence when vaccination begins, the duration of natural immunity, the trajectory of the epidemic prior to vaccination, and the level of healthcare available to effectively treat those with disease. Within a country we find that for a limited supply (doses for <20% of the population) the optimal strategy is to target the elderly. However, with a larger supply, if vaccination can occur while other interventions are maintained, the optimal strategy switches to targeting key transmitters to indirectly protect the vulnerable. As supply increases, vaccines that reduce or block infection have a greater impact than those that prevent disease alone due to the indirect protection provided to high-risk groups. Given a 2 billion global dose supply in 2021, we find that a strategy in which doses are allocated to countries proportional to population size is close to optimal in averting deaths and aligns with the ethical principles agreed in pandemic preparedness planning.

  • Journal article
    Da DF, McCabe R, Somé BM, Esperança PM, Sala KA, Blight J, Blagborough AM, Dowell F, Yerbanga SR, Lefèvre T, Mouline K, Dabiré RK, Churcher TSet al., 2021,

    Detection of Plasmodium falciparum in laboratory-reared and naturally infected wild mosquitoes using near-infrared spectroscopy.

    , Scientific Reports, Vol: 11, Pages: 10289-10289, ISSN: 2045-2322

    There is an urgent need for high throughput, affordable methods of detecting pathogens inside insect vectors to facilitate surveillance. Near-infrared spectroscopy (NIRS) has shown promise to detect arbovirus and malaria in the laboratory but has not been evaluated in field conditions. Here we investigate the ability of NIRS to identify Plasmodium falciparum in Anopheles coluzzii mosquitoes. NIRS models trained on laboratory-reared mosquitoes infected with wild malaria parasites can detect the parasite in comparable mosquitoes with moderate accuracy though fails to detect oocysts or sporozoites in naturally infected field caught mosquitoes. Models trained on field mosquitoes were unable to predict the infection status of other field mosquitoes. Restricting analyses to mosquitoes of uninfectious and highly-infectious status did improve predictions suggesting sensitivity and specificity may be better in mosquitoes with higher numbers of parasites. Detection of infection appears restricted to homogenous groups of mosquitoes diminishing NIRS utility for detecting malaria within mosquitoes.

  • Journal article
    Akala HM, Watson OJ, Mitei KK, Juma DW, Verity R, Ingasia LA, Opot BH, Okath RO, Chemwor GC, Juma JA, Mwakio EW, Brazeau N, Cheruiyot AC, Yeda RA, Maraka MN, Okello CO, Kateete DP, Managbanag JR, Andagalu B, Ogutu BR, Kamau Eet al., 2021,

    <i>Plasmodium</i> interspecies interactions during a period of increasing prevalence of <i>Plasmodium ovale</i> in symptomatic individuals seeking treatment: an observational study

    , LANCET MICROBE, Vol: 2, Pages: E141-E150
  • Journal article
    Fraser KJ, Mwandigha L, Traore SF, Traore MM, Doumbia S, Junnila A, Revay E, Beier JC, Marshall JM, Ghani AC, Muller Get al., 2021,

    Estimating the potential impact of Attractive Targeted Sugar Baits (ATSBs) as a new vector control tool for Plasmodium falciparum malaria

    , Malaria Journal, Vol: 20, ISSN: 1475-2875

    BackgroundAttractive targeted sugar baits (ATSBs) are a promising new tool for malaria control as they can target outdoor-feeding mosquito populations, in contrast to current vector control tools which predominantly target indoor-feeding mosquitoes.MethodsIt was sought to estimate the potential impact of these new tools on Plasmodium falciparum malaria prevalence in African settings by combining data from a recent entomological field trial of ATSBs undertaken in Mali with mathematical models of malaria transmission. The key parameter determining impact on the mosquito population is the excess mortality due to ATSBs, which is estimated from the observed reduction in mosquito catch numbers. A mathematical model capturing the life cycle of P. falciparum malaria in mosquitoes and humans and incorporating the excess mortality was used to estimate the potential epidemiological effect of ATSBs.ResultsThe entomological study showed a significant reduction of ~ 57% (95% CI 33–72%) in mosquito catch numbers, and a larger reduction of ~ 89% (95% CI 75–100%) in the entomological inoculation rate due to the fact that, in the presence of ATSBs, most mosquitoes do not live long enough to transmit malaria. The excess mortality due to ATSBs was estimated to be lower (mean 0.09 per mosquito per day, seasonal range 0.07–0.11 per day) than the bait feeding rate obtained from one-day staining tests (mean 0.34 per mosquito per day, seasonal range 0.28–0.38 per day).ConclusionsFrom epidemiological modelling, it was predicted that ATSBs could result in large reductions (> 30% annually) in prevalence and clinical incidence of malaria, even in regions with an existing high malaria burden. These results suggest that this new tool could provide a promising addition to existing vector control tools and result in significant reductions in malaria burden across a range of malaria-endemic settings.

  • Journal article
    Challenger J, Olivera Mesa D, Da DF, Yerbanga RS, Lefèvre T, Cohuet A, Churcher TSet al., 2021,

    Predicting the public health impact of a malaria transmission-blocking vaccine

    , Nature Communications, Vol: 12, Pages: 1-12, ISSN: 2041-1723

    Transmission-blocking vaccines that interrupt malaria transmission from humans to mosquitoes are being tested in early clinical trials. The activity of such a vaccine is commonly evaluated using membrane-feeding assays. Understanding the field efficacy of such a vaccine requires knowledge of how heavily infected wild, naturally blood-fed mosquitoes are, as this indicates how difficult it will be to block transmission. Here we use data on naturally infected mosquitoes collected in Burkina Faso to translate the laboratory-estimated activity into an estimated activity in the field. A transmission dynamics model is then utilised to predict a transmission-blocking vaccine’s public health impact alongside existing interventions. The model suggests that school-aged children are an attractive population to target for vaccination. Benefits of vaccination are distributed across the population, averting the greatest number of cases in younger children. Utilising a transmission-blocking vaccine alongside existing interventions could have a substantial impact against malaria.

  • Journal article
    Diawara H, Walker P, Cairns M, Steinhardt LC, Diawara F, Kamate B, Duval L, Sicuri E, Sagara I, Sadou A, Mihigo J, Eckert E, Dicko A, Conteh Let al., 2021,

    Cost-effectiveness of district-wide seasonal malaria chemoprevention when implemented through routine malaria control programme in Kita, Mali using fixed point distribution

    , Malaria Journal, Vol: 20, Pages: 1-14, ISSN: 1475-2875

    Background: Seasonal malaria chemoprevention (SMC) is a strategy for malaria control recommended by the World Health Organization (WHO) since 2012 for Sahelian countries. The Mali National Malaria Control Programme adopted a plan for pilot implementation and nationwide scale-up by 2016. Given that SMC is a relatively new approach, there is an urgent need to assess the costs and cost effectiveness of SMC when implemented through the routine health system to inform decisions on resource allocation.Methods: Cost data were collected from pilot implementation of SMC in Kita district, which targeted 77,497 children aged 3–59 months. Starting in August 2014, SMC was delivered by fixed point distribution in villages with the first dose observed each month. Treatment consisted of sulfadoxine-pyrimethamine and amodiaquine once a month for four consecutive months, or rounds. Economic and financial costs were collected from the provider perspective using an ingredients approach. Effectiveness estimates were based upon a published mathematical transmission model calibrated to local epidemiology, rainfall patterns and scale-up of interventions. Incremental cost effectiveness ratios were calculated for the cost per malaria episode averted, cost per disability adjusted life years (DALYs) averted, and cost per death averted.Results: The total economic cost of the intervention in the district of Kita was US $357,494. Drug costs and personnel costs accounted for 34% and 31%, respectively. Incentives (payment other than salary for efforts beyond routine activities) accounted for 25% of total implementation costs. Average financial and economic unit costs per child per round were US $0.73 and US $0.86, respectively; total annual financial and economic costs per child receiving SMC were US $2.92 and US $3.43, respectively. Accounting for coverage, the economic cost per child fully adherent (receiving all four rounds) was US $6.38 and US $4.69, if weighted highly adherent, (receivin

  • Journal article
    Winskill P, Mousa A, Oresanya O, Counihan H, Okell L, Walker Pet al., 2021,

    Does integrated community case management (iCCM) target health inequities and treatment delays? Evidence from an analysis of Demographic and Health Surveys data from 21 countries in the period 2010 to 2018

    , Journal of Global Health, Vol: 11, Pages: 1-10, ISSN: 2047-2978

    BackgroundIntegrated community case management (iCCM) is a programme that can, via community health workers (CHWs), increase access to timely and essential treatments for children. As well as improving treatment coverage, iCCM has an additional equity-focus with the aim of targetingunderserved populations. To assess the success of iCCM programmes it is important that we understand the contribution they are making to equitable health coverage.MethodsWe analysed demographic and health survey data from 21 countries over 9 years to assess evidence and evaluate iCCM programmes. We summarise the contribution CHWs are making relative to other healthcare provider groups and what treatment combinations CHWs are commonly prescribing. We assessed the ability of CHWs to target treatment delays and health inequities by evaluating time to treatment following fever onset and relationships between CHWs and wealth, rurality and remoteness.ResultsThere was good evidence that CHWs are being successfully targeted to improve inequities in healthcare coverage. There is a larger contribution of CHWs in areas with higher poverty, rurality and remoteness. In six surveys CHWs were associated with significantly shorter average timebetween fever onset and advice or treatment seeking, whilst in one they were associated with significantly longer times. In areas with active CHW programmes, the contribution of CHWs relative to other healthcare provider groups varied between 11% to 45% of treatment visits. The distribution of types of treatment provided by CHWs was also very variable between countries.ConclusionsThe success of an iCCM programme depends not only on increasing treatment coverage but addressing inequities in access to timely healthcare. Whilst much work is still needed to attain universal healthcare targets, and despite incomplete data, there is evidence that iCCM is successfully addressing treatment delays and targeting underserved populations.

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