Imperial College London

ProfessorTimothyHallett

Faculty of MedicineSchool of Public Health

Professor of Global Health
 
 
 
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Contact

 

+44 (0)20 7594 1150timothy.hallett

 
 
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Location

 

Norfolk PlaceSt Mary's Campus

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Summary

 

Publications

Publication Type
Year
to

212 results found

Stover J, Hallett TB, Wu Z, Warren M, Gopalappa C, Pretorius C, Ghys PD, Montaner J, Schwartlander Bet al., 2014, How Can We Get Close to Zero? The Potential Contribution of Biomedical Prevention and the Investment Framework towards an Effective Response to HIV, PLOS One, Vol: 9, ISSN: 1932-6203

Background: In 2011 an Investment Framework was proposed that described how the scale-up of key HIV interventionscould dramatically reduce new HIV infections and deaths in low and middle income countries by 2015. This frameworkincluded ambitious coverage goals for prevention and treatment services resulting in a reduction of new HIV infections bymore than half. However, it also estimated a leveling in the number of new infections at about 1 million annually after 2015.Methods: We modeled how the response to AIDS can be further expanded by scaling up antiretroviral treatment (ART)within the framework provided by the 2013 WHO treatment guidelines. We further explored the potential contributions ofnew prevention technologies: ‘Test and Treat’, pre-exposure prophylaxis and an HIV vaccine.Findings: Immediate aggressive scale up of existing approaches including the 2013 WHO guidelines could reduce newinfections by 80%. A ‘Test and Treat’ approach could further reduce new infections. This could be further enhanced by afuture highly effective pre-exposure prophylaxis and an HIV vaccine, so that a combination of all four approaches couldreduce new infections to as low as 80,000 per year by 2050 and annual AIDS deaths to 260,000.Interpretation: In a set of ambitious scenarios, we find that immediate implementation of the 2013 WHO antiretroviraltherapy guidelines could reduce new HIV infections by 80%. Further reductions may be achieved by moving to a ‘Test andTreat’ approach, and eventually by adding a highly effective pre-exposure prophylaxis and an HIV vaccine, if they becomeavailable.

Journal article

Hallett TB, Zaba B, Stover J, Brown T, Slaymaker E, Gregson S, Wilson DP, Case KKet al., 2014, Embracing different approaches to estimating HIV incidence, prevalence and mortality, AIDS, Vol: 28, Pages: S523-S532, ISSN: 0269-9370

Journal article

Anderson S-J, Harper M, Kilonzo N, Hallett TBet al., 2014, Maximising the effect of combination HIV prevention in Kenya (vol 384, pg 1426, 2014), LANCET, Vol: 384, Pages: 1576-1576, ISSN: 0140-6736

Journal article

Vesga JF, Cori A, van Sighem A, Hallett TBet al., 2014, Estimating HIV incidence from case-report data: method and an application in Colombia, AIDS, Vol: 28, Pages: S489-S496, ISSN: 0269-9370

Journal article

Eaton JW, Rehle TM, Jooste S, Nkambule R, Kim AA, Mahy M, Hallett TBet al., 2014, Recent HIV prevalence trends among pregnant women and all women in sub-Saharan Africa: implications for HIV estimates, AIDS, Vol: 28, Pages: S507-S514, ISSN: 0269-9370

Objectives: National population-wide HIV prevalence and incidence trends in sub-Saharan Africa (SSA) are indirectly estimated using HIV prevalence measured among pregnant women attending antenatal clinics (ANC), among other data. We evaluated whether recent HIV prevalence trends among pregnant women are representative of general population trends.Design: Serial population-based household surveys in 13 SSA countries.Methods: We calculated HIV prevalence trends among all women aged 15–49 years and currently pregnant women between surveys conducted from 2003 to 2008 (period 1) and 2009 to 2012 (period 2). Log-binomial regression was used to test for a difference in prevalence trend between the two groups. Prevalence among pregnant women was age-standardized to represent the age distribution of all women.Results: Pooling data for all countries, HIV prevalence declined among pregnant women from 6.5 [95% confidence interval (CI) 5.3–7.9%] to 5.3% (95% CI 4.2–6.6%) between periods 1 and 2, whereas it remained unchanged among all women at 8.4% (95% CI 8.0–8.9%) in period 1 and 8.3% (95% CI 7.9–8.8%) in period 2. Prevalence declined by 18% (95% CI -9–38%) more in pregnant women than nonpregnant women. Estimates were similar in Western, Eastern, and Southern regions of SSA; none were statistically significant (P > 0.05). HIV prevalence decreased significantly among women aged 15–24 years while increasing significantly among women 35–49 years, who represented 29% of women but only 15% of pregnant women. Age-standardization of prevalence in pregnant women did not reconcile the discrepant trends because at older ages prevalence was lower among pregnant women than nonpregnant women.Conclusion: As HIV prevalence in SSA has shifted toward older, less-fertile women, HIV prevalence among pregnant women has declined more rapidly than prevalence in women overall. Interpretation of ANC prevalence data to inform national HIV estimates sh

Journal article

Bao L, Ye J, Hallett TB, 2014, Incorporating incidence information within the UNAIDS Estimation and Projection Package framework: a study based on simulated incidence assay data, AIDS, Vol: 28, Pages: S515-S522, ISSN: 0269-9370

Journal article

Case KK, Hallett TB, Gregson S, Porter K, Ghys PDet al., 2014, Development and future directions for the Joint United Nations Programme on HIV/AIDS estimates, AIDS, Vol: 28, Pages: S411-S414, ISSN: 0269-9370

Journal article

Anderson S-J, Harper M, Kilonzo N, Hallett TBet al., 2014, Maximising the effect of combination HIV prevention in Kenya--Authors' reply., Lancet, Vol: 384, Pages: 1426-1427

Journal article

Dimitrov D, Boily M-C, Hallett TB, 2014, How Much Do We Know about Drug Resistance Due to PrEP Use? Analysis of Experts' Opinion and Its Influence on the Projected Public Health Impact, Symposium on HIV Research for Prevention (HIV R4P), Publisher: MARY ANN LIEBERT, INC, Pages: A161-A161, ISSN: 0889-2229

Conference paper

Jones A, Cremin I, Abdullah F, Idoko J, Cherutich P, Kilonzo N, Rees H, Hallett T, O'Reilly K, Koechlin F, Schwartlander B, de Zalduondo B, Kim S, Jay J, Huh J, Piot P, Dybul Met al., 2014, Transformation of HIV from pandemic to low-endemic levels: a public health approach to combination prevention, LANCET, Vol: 384, Pages: 272-279, ISSN: 0140-6736

Journal article

Anderson S-J, Cherutich P, Kilonzo N, Cremin I, Fecht D, Kimanga D, Harper M, Masha RL, Ngongo PB, Maina W, Dybul M, Hallett TBet al., 2014, Maximising the effect of combination HIV prevention through prioritisation of the people and places in greatest need: a modelling study, LANCET, Vol: 384, Pages: 249-256, ISSN: 0140-6736

Journal article

Hallett TB, Eaton JW, Menzies N, 2014, Beware of using invalid transmission models to guide HIV health policy Reply, LANCET GLOBAL HEALTH, Vol: 2, Pages: E261-E261, ISSN: 2214-109X

Journal article

Martin NK, Devine A, Eaton JW, Hallett TB, Foster GR, Dore GJ, Easterbrook PJ, Legood R, Vickerman Pet al., 2014, MODELING THE IMPACT OF EARLY ANTIRETROVIRAL THERAPY FOR ADULTS COINFECTED WITH HIV AND HEPATITIS B OR C IN SOUTH AFRICA, 49th Annual International Liver Congress of the European-Association-for-the-Study-of-the-Liver, Publisher: ELSEVIER SCIENCE BV, Pages: S483-S483, ISSN: 0168-8278

Conference paper

Nayagam S, Shimakawa Y, Lemoine M, Njie R, Tamba S, D'Alessandro U, Hallett T, Conteh L, Thursz Met al., 2014, FEASIBILITY AND COST ANALYSIS OF COMMUNITY BASED HEPATITIS B SCREENING PROGRAMME IN SUB-SAHARAN AFRICA, 49th Annual International Liver Congress of the European-Association-for-the-Study-of-the-Liver, Publisher: ELSEVIER SCIENCE BV, Pages: S36-S36, ISSN: 0168-8278

Conference paper

Smith J, Nyamukapa C, Gregson S, Lewis J, Magutshwa S, Schumacher C, Mushati P, Hallett T, Garnett Get al., 2014, The Distribution of Sex Acts and Condom Use within Partnerships in a Rural Sub-Saharan African Population, PLOS ONE, Vol: 9, ISSN: 1932-6203

Journal article

Ralph L, McCoy S, Hallett T, Padian Net al., 2014, Research on hormonal contraception and HIV Reply, LANCET, Vol: 383, Pages: 305-306, ISSN: 0140-6736

Journal article

Birger RB, Hallett TB, Sinha A, Grenfell BT, Hodder SLet al., 2014, Modeling the Impact of Interventions Along the HIV Continuum of Care in Newark, New Jersey, CLINICAL INFECTIOUS DISEASES, Vol: 58, Pages: 274-284, ISSN: 1058-4838

Journal article

Braithwaite RS, Nucifora KA, Toohey C, Kessler J, Uhler LM, Mentor SM, Keebler D, Hallett Tet al., 2014, How do different eligibility guidelines for antiretroviral therapy affect the cost-effectiveness of routine viral load testing in sub-Saharan Africa?, AIDS, Vol: 28, Pages: S73-S83, ISSN: 0269-9370

Journal article

Hallett TB, Menzies NA, Revill P, Keebler D, Borquez A, McRobie E, Eaton JWet al., 2014, Using modeling to inform international guidelines for antiretroviral treatment, AIDS, Vol: 28, Pages: S1-S4, ISSN: 0269-9370

Journal article

Pretorius C, Menzies NA, Chindelevitch L, Cohen T, Cori A, Eaton JW, Fraser C, Gopalappa C, Hallett TB, Salomon JA, Stover J, White RG, Dodd PJet al., 2014, The potential effects of changing HIV treatment policy on tuberculosis outcomes in South Africa: results from three tuberculosis-HIV transmission models, AIDS, Vol: 28, Pages: S25-S34, ISSN: 0269-9370

Journal article

Martin NK, Devine A, Eaton JW, Miners A, Hallett TB, Foster GR, Dore GJ, Easterbrook PJ, Legood R, Vickerman Pet al., 2014, Modeling the impact of early antiretroviral therapy for adults coinfected with HIV and hepatitis B or C in South Africa, AIDS, Vol: 28, Pages: S35-S46, ISSN: 0269-9370

Journal article

Eaton JW, Menzies NA, Stover J, Cambiano V, Chindelevitch L, Cori A, Hontelez JAC, Humair S, Kerr CC, Klein DJ, Mishra S, Mitchell KM, Nichols BE, Vickerman P, Bakker R, Baernighausen T, Bershteyn A, Bloom DE, Boily M-C, Chang ST, Cohen T, Dodd PJ, Fraser C, Gopalappa C, Lundgren J, Martin NK, Mikkelsen E, Mountain E, Pham QD, Pickles M, Phillips A, Platt L, Pretorius C, Prudden HJ, Salomon JA, van de Vijver DAMC, de Vlas SJ, Wagner BG, White RG, Wilson DP, Zhang L, Blandford J, Meyer-Rath G, Remme M, Revill P, Sangrujee N, Terris-Prestholt F, Doherty M, Shaffer N, Easterbrook PJ, Hirnschall G, Hallett TBet al., 2014, Health benefits, costs, and cost-effectiveness of earlier eligibility for adult antiretroviral therapy and expanded treatment coverage: a combined analysis of 12 mathematical models, LANCET GLOBAL HEALTH, Vol: 2, Pages: E23-E34, ISSN: 2214-109X

Journal article

Keebler D, Revill P, Braithwaite S, Phillips A, Blaser N, Borquez A, Cambiano V, Ciaranello A, Estill J, Gray R, Hill A, Keiser O, Kessler J, Menzies NA, Nucifora KA, Vizcaya LS, Walker S, Welte A, Easterbrook P, Doherty M, Hirnschall G, Hallett TBet al., 2014, Cost-effectiveness of different strategies to monitor adults on antiretroviral treatment: a combined analysis of three mathematical models, LANCET GLOBAL HEALTH, Vol: 2, Pages: E35-E43, ISSN: 2214-109X

Journal article

Eaton JW, Menzies NA, Stover J, Cambiano V, Chindelevitch L, Cori A, Hontelez JAC, Humair S, Kerr CC, Klein DJ, Mishra S, Mitchell KM, Nichols BE, Vickerman P, Bakker R, Bärnighausen T, Bershteyn A, Bloom DE, Boily M-C, Chang ST, Cohen T, Dodd PJ, Fraser C, Gopalappa C, Lundgren J, Martin NK, Mikkelsen E, Mountain E, Pham QD, Pickles M, Phillips A, Platt L, Pretorius C, Prudden HJ, Salomon JA, van de Vijver DAMC, de Vlas SJ, Wagner BG, White RG, Wilson DP, Zhang L, Blandford J, Meyer-Rath G, Remme M, Revill P, Sangrujee N, Terris-Prestholt F, Doherty M, Shaffer N, Easterbrook PJ, Hirnschall G, Hallett TBet al., 2014, Health benefits, costs, and cost-effectiveness of earlier eligibility for adult antiretroviral therapy and expanded treatment coverage: a combined analysis of 12 mathematical models., Lancet Glob Health, Vol: 2, Pages: e23-e34

BACKGROUND: New WHO guidelines recommend initiation of antiretroviral therapy for HIV-positive adults with CD4 counts of 500 cells per μL or less, a higher threshold than was previously recommended. Country decision makers have to decide whether to further expand eligibility for antiretroviral therapy accordingly. We aimed to assess the potential health benefits, costs, and cost-effectiveness of various eligibility criteria for adult antiretroviral therapy and expanded treatment coverage. METHODS: We used several independent mathematical models in four settings-South Africa (generalised epidemic, moderate antiretroviral therapy coverage), Zambia (generalised epidemic, high antiretroviral therapy coverage), India (concentrated epidemic, moderate antiretroviral therapy coverage), and Vietnam (concentrated epidemic, low antiretroviral therapy coverage)-to assess the potential health benefits, costs, and cost-effectiveness of various eligibility criteria for adult antiretroviral therapy under scenarios of existing and expanded treatment coverage, with results projected over 20 years. Analyses assessed the extension of eligibility to include individuals with CD4 counts of 500 cells per μL or less, or all HIV-positive adults, compared with the previous (2010) recommendation of initiation with CD4 counts of 350 cells per μL or less. We assessed costs from a health-system perspective, and calculated the incremental cost (in US$) per disability-adjusted life-year (DALY) averted to compare competing strategies. Strategies were regarded very cost effective if the cost per DALY averted was less than the country's 2012 per-head gross domestic product (GDP; South Africa: $8040; Zambia: $1425; India: $1489; Vietnam: $1407) and cost effective if the cost per DALY averted was less than three times the per-head GDP. FINDINGS: In South Africa, the cost per DALY averted of extending eligibility for antiretroviral therapy to adult patients with CD4 counts of 500 cells per μL

Journal article

Vassall A, Remme M, Watts C, Hallett T, Siapka M, Vickerman P, Terris-Prestholt F, Haacker M, Heise L, Haines A, Atun R, Piot Pet al., 2013, Financing Essential HIV Services: A New Economic Agenda, PLOS MEDICINE, Vol: 10, ISSN: 1549-1277

Journal article

Hallett TB, 2013, Early HIV Infection in the United States: A Virus's Eye View, PLOS MEDICINE, Vol: 10, ISSN: 1549-1277

Journal article

van de Vijver DAMC, Nichols BE, Abbas UL, Boucher CAB, Cambiano V, Eaton JW, Glaubius R, Lythgoe K, Mellors J, Phillips A, Sigaloff KC, Hallett TBet al., 2013, Preexposure prophylaxis will have a limited impact on HIV-1 drug resistance in sub-Saharan Africa: a comparison of mathematical models, AIDS, Vol: 27, Pages: 2943-2951, ISSN: 0269-9370

Journal article

van de Vijver DA, Nichols BE, Abbas UL, Boucher CA, Cambiano V, Eaton JW, Glaubius R, Lythgoe K, Mellors J, Phillips A, Sigaloff KC, Hallett TBet al., 2013, Pre-exposure prophylaxis (PrEP) will have a limited impact on the prevalence of HIV-1 drug resistance in sub-Saharan Africa: comparison of mathematical models, AIDS, Vol: 27, Pages: 2943-2951, ISSN: 0269-9370

BACKGROUND: Preexposure prophylaxis (PrEP) with tenofovir and emtricitabine can prevent new HIV-1 infections, but there is a concern that use of PrEP could increase HIV drug resistance resulting in loss of treatment options. We compared standardized outcomes from three independent mathematical models simulating the impact of PrEP on HIV transmission and drug resistance in sub-Saharan African countries.METHODS: All models assume that people using PrEP receive an HIV test every 3-6 months. The models vary in structure and parameter choices for PrEP coverage, effectiveness of PrEP (at different adherence levels) and the rate with which HIV drug resistance emerges and is transmitted.RESULTS: The models predict that the use of PrEP in conjunction with antiretroviral therapy will result in a lower prevalence of HIV than when only antiretroviral therapy is used. With or without PrEP, all models suggest that HIV drug resistance will increase over the next 20 years due to antiretroviral therapy. PrEP will increase the absolute prevalence of drug resistance in the total population by less than 0.5% and amongst infected individuals by at most 7%. Twenty years after the introduction of PrEP, the majority of drug-resistant infections is due to antiretroviral therapy (50-63% across models), whereas 40-50% will be due to transmission of drug resistance, and less than 4% to the use of PrEP.CONCLUSION: HIV drug resistance resulting from antiretroviral therapy is predicted to far exceed that resulting from PrEP. Concern over drug resistance should not be a reason to limit the use of PrEP.

Journal article

Dimitrov D, Boily M-C, Brown ER, Hallett TBet al., 2013, Analytic Review of Modeling Studies of ARV Based PrEP Interventions Reveals Strong Influence of Drug-Resistance Assumptions on the Population-Level Effectiveness, PLOS One, Vol: 8, ISSN: 1932-6203

BackgroundFour clinical trials have shown that oral and topical pre-exposure prophylaxis (PrEP) based on tenofovir may be effective in preventing HIV transmission. The expected reduction in HIV transmission and the projected prevalence of drug resistance due to PrEP use vary significantly across modeling studies as a result of the broad spectrum of assumptions employed. Our goal is to quantify the influence of drug resistance assumptions on the predicted population-level impact of PrEP.MethodsAll modeling studies which evaluate the impact of oral or topical PrEP are reviewed and key assumptions regarding mechanisms of generation and spread of drug-resistant HIV are identified. A dynamic model of the HIV epidemic is developed to assess and compare the impact of oral PrEP using resistance assumptions extracted from published studies. The benefits and risks associated with ten years of PrEP use are evaluated under identical epidemic, behavioral and intervention conditions in terms of cumulative fractions of new HIV infections prevented, resistance prevalence among those infected with HIV, and fractions of infections in which resistance is transmitted.ResultsPublished models demonstrate enormous variability in resistance-generating assumptions and uncertainty in parameter values. Depending on which resistance parameterization is used, a resistance prevalence between 2% and 44% may be expected if 50% efficacious oral PrEP is used consistently by 50% of the population over ten years. We estimated that resistance may be responsible for up to a 10% reduction or up to a 30% contribution to the fraction of prevented infections predicted in different studies.ConclusionsResistance assumptions used in published studies have a strong influence on the projected impact of PrEP. Modelers and virologists should collaborate toward clarifying the set of resistance assumptions biologically relevant to the PrEP products which are already in use or soon to be added to the arsenal against

Journal article

Ralph LJ, McCoy SI, Hallett T, Padian Net al., 2013, Next steps for research on hormonal contraception and HIV, LANCET, Vol: 382, Pages: 1467-1469, ISSN: 0140-6736

Journal article

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