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Potential impact of multiple interventions on HIV incidence in a hyperendemic region in Western Kenya: a modelling study.
BMC Infectious Diseases. 2016 Apr 29; 16:189.BACKGROUND: Multiple prevention interventions, including early antiretroviral therapy initiation, may reduce HIV incidence in hyperendemic settings. Our aim was to predict the short-term impact of various single and combined interventions on HIV spreading in the adult population of Ndhiwa subcounty (Nyanza Province, Kenya). METHODS: A mathematical model was used with data on adults (15-59 years) from the Ndhiwa HIV Impact in Population Survey to compare the impacts on HIV prevalence, HIV incidence rate, and population viral load suppression of various interventions. These interventions included: improving the cascade of care (use of three guidelines), increasing voluntary medical male circumcision (VMMC), and implementing pre-exposure prophylaxis (PrEP) use among HIV-uninfected women. RESULTS: After four years, improving separately the cascade of care under the WHO 2013 guidelines and under the treat-all strategy would reduce the overall HIV incidence rate by 46 and 58 %, respectively, vs. the baseline rate, and by 35 and 49 %, respectively, vs. the implementation of the current Kenyan guidelines. With conservative and optimistic scenarios, VMMC and PrEP would reduce the HIV incidence rate by 15-25 % and 22-28 % vs. the baseline, respectively. Combining the WHO 2013 guidelines with VMMC would reduce the HIV incidence rate by 35-56 % and combining the treat-all strategy with VMMC would reduce it by 49-65 %. Combining the WHO 2013 guidelines, VMMC, and PrEP would reduce the HIV incidence rate by 46-67 %. CONCLUSIONS: The impacts of the WHO 2013 guidelines and the treat-all strategy were relatively close; their implementation is desirable to reduce HIV spread. Combining several strategies is promising in adult populations of hyperendemic areas but requires regular, reliable, and costly monitoring.
Population-level impact of an accelerated HIV response plan to reach the UNAIDS 90-90-90 target in Cote d'Ivoire: Insights from mathematical modeling.
PLoS Medicine. 2017 Jun; 14(6):e1002321.BACKGROUND: National responses will need to be markedly accelerated to achieve the ambitious target of the Joint United Nations Programme on HIV/AIDS (UNAIDS). This target aims for 90% of HIV-positive individuals to be aware of their status, for 90% of those aware to receive antiretroviral therapy (ART), and for 90% of those on treatment to have a suppressed viral load by 2020, with each individual target reaching 95% by 2030. We aimed to estimate the impact of various treatment-as-prevention scenarios in Cote d'Ivoire, one of the countries with the highest HIV incidence in West Africa, with unmet HIV prevention and treatment needs, and where key populations are important to the broader HIV epidemic. METHODS AND FINDINGS: An age-stratified dynamic model was developed and calibrated to epidemiological and programmatic data using a Bayesian framework. The model represents sexual and vertical HIV transmission in the general population, female sex workers (FSW), and men who have sex with men (MSM). We estimated the impact of scaling up interventions to reach the UNAIDS targets, as well as the impact of 8 other scenarios, on HIV transmission in adults and children, compared to our baseline scenario that maintains 2015 rates of testing, ART initiation, ART discontinuation, treatment failure, and levels of condom use. In 2015, we estimated that 52% (95% credible intervals: 46%-58%) of HIV-positive individuals were aware of their status, 72% (57%-82%) of those aware were on ART, and 77% (74%-79%) of those on ART were virologically suppressed. Reaching the UNAIDS targets on time would avert 50% (42%-60%) of new HIV infections over 2015-2030 compared to 30% (25%-36%) if the 90-90-90 target is reached in 2025. Attaining the UNAIDS targets in FSW, their clients, and MSM (but not in the rest of the population) would avert a similar fraction of new infections (30%; 21%-39%). A 25-percentage-point drop in condom use from the 2015 levels among FSW and MSM would reduce the impact of reaching the UNAIDS targets, with 38% (26%-51%) of infections averted. The study's main limitation is that homogenous spatial coverage of interventions was assumed, and future lines of inquiry should examine how geographical prioritization could affect HIV transmission. CONCLUSIONS: Maximizing the impact of the UNAIDS targets will require rapid scale-up of interventions, particularly testing, ART initiation, and limiting ART discontinuation. Reaching clients of FSW, as well as key populations, can efficiently reduce transmission. Sustaining the high condom-use levels among key populations should remain an important prevention pillar.
Individualizing the WHO HIV and infant feeding guidelines: optimal breastfeeding duration to maximize infant HIV-free survival.
AIDS. 2014 Jul; 28 Suppl 3:S287-99.OBJECTIVES: To determine how infant feeding recommendations can maximize HIV-free survival (HFS) among HIV-exposed, uninfected African infants, balancing risks of breast milk-associated HIV infection with setting-specific risks of illness and death associated with replacement feeding. DESIGN: Validated mathematical model of HIV-exposed, uninfected infants, with published data from Africa. METHODS: We projected 24-month HFS using combinations of: maternal CD4, antiretroviral drug availability, and relative risk of mortality among replacement-fed compared to breastfed infants ('RR-RF', range 1.0-6.0). For each combination, we identified the 'optimal' breastfeeding duration (0-24 months) maximizing HFS. We compared HFS under an 'individualized' approach, based on the above parameters, to the WHO 'public health approach' (12 months breastfeeding for all HIV-infected women). RESULTS: Projected HFS was 65-93%. When the value of RR-RF is 1.0, replacement feeding from birth maximized HFS. At a commonly reported RR-RF value (2.0), optimal breastfeeding duration was 3-12 months, depending on maternal CD4 and antiretroviral drug availability. As the value of RR-RF increased, optimal breastfeeding duration increased. Compared to the public health approach, an individualized approach improved absolute HFS by less than 1% if RR-RF value was 2.0-4.0, by 3% if RR-RF value was 1.0 or 6.0, and by greater amounts if access to antiretroviral drugs was limited. CONCLUSION: Tailoring breastfeeding duration to maternal CD4, antiretroviral drug availability, and local replacement feeding safety can optimize HFS among HIV-exposed infants. An individualized approach leads to moderate gains in HFS, but only when mortality risks from replacement feeding are very low or very high, or antiretroviral drug availability is limited. The WHO public health approach is beneficial in most resource-limited settings.
Can the UNAIDS modes of transmission model be improved? A comparison of the original and revised model projections using data from a setting in west Africa.
AIDS. 2013 Oct 23; 27(16):2623-35.OBJECTIVE: The UNAIDS modes of transmission model (MoT) is a user-friendly model, developed to predict the distribution of new HIV infections among different subgroups. The model has been used in 29 countries to guide interventions. However, there is the risk that the simplifications inherent in the MoT produce misleading findings. Using input data from Nigeria, we compare projections from the MoT with those from a revised model that incorporates additional heterogeneity. METHODS: We revised the MoT to explicitly incorporate brothel and street-based sex-work, transactional sex, and HIV-discordant couples. Both models were parameterized using behavioural and epidemiological data from Cross River State, Nigeria. Model projections were compared, and the robustness of the revised model projections to different model assumptions, was investigated. RESULTS: The original MoT predicts 21% of new infections occur in most-at-risk-populations (MARPs), compared with 45% (40-75%, 95% Crl) once additional heterogeneity and updated parameterization is incorporated. Discordant couples, a subgroup previously not explicitly modelled, are predicted to contribute a third of new HIV infections. In addition, the new findings suggest that women engaging in transactional sex may be an important but previously less recognized risk group, with 16% of infections occurring in this subgroup. CONCLUSION: The MoT is an accessible model that can inform intervention priorities. However, the current model may be potentially misleading, with our comparisons in Nigeria suggesting that the model lacks resolution, making it challenging for the user to correctly interpret the nature of the epidemic. Our findings highlight the need for a formal review of the MoT.
Sexually Transmitted Infections. 2010 Dec; 86 Suppl 2:ii93-9.BACKGROUND: Every 2 years, the Joint United Nations Programme on HIV/AIDS (UNAIDS) produces probabilistic estimates and projections of HIV prevalence rates for countries with generalised HIV/AIDS epidemics. To do this they use a simple epidemiological model and data from antenatal clinics and household surveys. The estimates are made using the Bayesian melding method, implemented by the incremental mixture importance sampling technique. This methodology is referred to as the 'estimation and projection package (EPP) model'. This has worked well for estimating and projecting prevalence in most countries. However, there has recently been an 'uptick' in prevalence in Uganda after a long sustained decline, which the EPP model does not predict. METHODS: To address this problem, a modification of the EPP model, called the 'r stochastic model' is proposed, in which the infection rate is allowed to vary randomly in time and is applied to the entire non-infected population. RESULTS: The resulting method yielded similar estimates of past prevalence to the EPP model for four countries and also similar median ('best') projections, but produced prediction intervals whose widths increased over time and that allowed for the possibility of an uptick after a decline. This seems more realistic given the recent Ugandan experience.
The African Development Bank, structural adjustment, and child mortality: a cross-national analysis of Sub-Saharan Africa.
International Journal of Health Services. 2013; 43(2):337-61.We conduct a cross-national analysis to test the hypothesis that African Development Bank (AfDB) structural adjustment adversely impacts child mortality in Sub-Saharan Africa. We use generalized least square random effects regression models and two-step Heckman models that correct for selection bias using data on 35 nations with up to four time points (1990, 1995, 2000, and 2005). We find substantial support for our hypothesis, which indicates that Sub-Saharan African nations that receive an AfDB structural adjustment loan tend to have higher levels of child mortality than Sub-Saharan African nations that do not receive such a loan. This finding remains stable even when controlling for selection bias on whether or not a Sub-Saharan African nation receives an AfDB structural adjustment loan. We conclude by discussing the methodological implications of the article, policy suggestions, and possible directions for future research.
Child mortality estimation: Methods used to adjust for bias due to AIDS in estimating trends in under-five mortality.
PLOS Medicine. 2012 Aug; 9(8):e1001298.In most low- and middle-income countries, child mortality is estimated from data provided by mothers concerning the survival of their children using methods that assume no correlation between the mortality risks of the mothers and those of their children. This assumption is not valid for populations with generalized HIV epidemics, however, and in this review, we show how the United Nations Inter-agency Group for Child Mortality Estimation (UN IGME) uses a cohort component projection model to correct for AIDS-related biases in the data used to estimate trends in under-five mortality. In this model, births in a given year are identified as occurring to HIV-positive or HIV-negative mothers, the lives of the infants and mothers are projected forward using survivorship probabilities to estimate survivors at the time of a given survey, and the extent to which excess mortality of children goes unreported because of the deaths of HIV-infected mothers prior to the survey is calculated. Estimates from the survey for past periods can then be adjusted for the estimated bias. The extent of the AIDS-related bias depends crucially on the dynamics of the HIV epidemic, on the length of time before the survey that the estimates are made for, and on the underlying non-AIDS child mortality. This simple methodology (which does not take into account the use of effective antiretroviral interventions) gives results qualitatively similar to those of other studies.
The impact of the new WHO antiretroviral treatment guidelines on HIV epidemic dynamics and cost in South Africa.
PloS One. 2011; 6(7):e21919.BACKGROUND: Since November 2009, WHO recommends that adults infected with HIV should initiate antiretroviral therapy (ART) at CD4+ cell counts of =350 cells/microl rather than =200 cells/microl. South Africa decided to adopt this strategy for pregnant and TB co-infected patients only. We estimated the impact of fully adopting the new WHO guidelines on HIV epidemic dynamics and associated costs. METHODS AND FINDING: We used an established model of the transmission and control of HIV in specified sexual networks and healthcare settings. We quantified the model to represent Hlabisa subdistrict, KwaZulu-Natal, South Africa. We predicted the HIV epidemic dynamics, number on ART and program costs under the new guidelines relative to treating patients at =200 cells/microl for the next 30 years. During the first five years, the new WHO treatment guidelines require about 7% extra annual investments, whereas 28% more patients receive treatment. Furthermore, there will be a more profound impact on HIV incidence, leading to relatively less annual costs after seven years. The resulting cumulative net costs reach a break-even point after on average 16 years. CONCLUSIONS: Our study strengthens the WHO recommendation of starting ART at =350 cells/microl for all HIV-infected patients. Apart from the benefits associated with many life-years saved, a modest frontloading appears to lead to net savings within a limited time-horizon. This finding is robust to alternative assumptions and foreseeable changes in ART prices and effectiveness. Therefore, South Africa should aim at rapidly expanding its healthcare infrastructure to fully embrace the new WHO guidelines.
South African Medical Journal. 2009 Jan; 99(1):12.Add to my documents.
Progress and challenges in modelling country-level HIV/AIDS epidemics: the UNAIDS Estimation and Projection Package 2007.
Sexually Transmitted Infections. 2008; 84(Suppl 1):i5-i10.The UNAIDS Estimation and Projection Package (EPP) was developed to aid in country-level estimation and shortterm projection of HIV/AIDS epidemics. This paper describes advances reflected in the most recent update of this tool (EPP 2007), and identifies key issues that remain to be addressed in future versions. The major change to EPP 2007 is the addition of uncertainty estimation for generalised epidemics using the technique of Bayesian melding, but many additional changes have been made to improve the user interface and efficiency of the package. This paper describes the interface for uncertainty analysis, changes to the user interface for calibration procedures and other user interface changes to improve EPP's utility in different settings. While formal uncertainty assessment remains an unresolved challenge in low-level and concentrated epidemics, the Bayesian melding approach has been applied to provide analysts in these settings with a visual depiction of the range of models that may be consistent with their data. In fitting the model to countries with longer-running epidemics in sub-Saharan Africa, a number of limitations have been identified in the current model with respect to accommodating behaviour change and accurately replicating certain observed epidemic patterns. This paper discusses these issues along with their implications for future changes to EPP and to the underlying UNAIDS Reference Group model.
Appropriate infant feeding practices result in better growth of infants and young children in rural Bangladesh.
American Journal of Clinical Nutrition. 2008 Jun; 87(6):1852-1859.The World Health Organization and the United Nations International Children's Emergency Fund recommend a global strategy for feeding infants and young children for proper nutrition and health. We evaluated the effects of following current infant feeding recommendations on the growth of infants and young children in rural Bangladesh. The prospective cohort study involved 1343 infants with monthly measurements on infant feeding practices (IFPs) and anthropometry at 17 occasions from birth to 24 mo of age to assess the main outcomes of weight, length, anthropometric indexes, and undernutrition. We created infant feeding scales relative to the infant feeding recommendations and modeled growth trajectories with the use of multilevel models for change. Mean (+or- SD) birth weight was 2697 +or- 401 g; 30%weighed less than 2500 g. Mean body weight at 12 and 24 mo was 7.9 +or- 1.1 kg and 9.7 +or- 1.3 kg, respectively. More appropriate IFPs were associated (P less than 0.001) with greater gain in weight andlength during infancy. Prior IFPs were also positively associated (P less than 0.005) with subsequent growth in weight during infancy. Children who were in the 75th percentile of the infant feeding scales had greater (P less than 0.05) attained weight and weight-for-age z scores and lower proportions of underweight compared with children who were in the 25th percentile of these scales. Our results provide strong evidence for the positive effects of following the current infant feeding recommendations on growth of infants and young children. Intervention programs should strive to improve conditions for enhancing current infant feeding recommendations, particularly in low-income countries. (author's)
Washington, D.C., World Bank, Latin America and the Caribbean Region, Human Development Department, 2007 Oct. 55 p. (Policy Research Working Paper No. 4377)A new literature on the nature of and policies for youth in Latin America is emerging, but there is still very little known about who are the most vulnerable young people. This paper aims to characterize the heterogeneity in the youth population and identify ex ante the youth that are at-risk and should be targeted with prevention programs. Using non-parametric methodologies and specialized youth surveys from Mexico and Chile, the authors quantify and characterize the different subgroups of youth, according to the amount of risk in their lives, and find that approximately 20 percent of 18 to 24 year old Chileans and 40 percent of the same age cohort in Mexico are suffering the consequences of a range of negative behaviors. Another 8 to 20 percent demonstrate factors in their lives that pre-dispose them to becoming at-risk youth - they are the candidates for prevention programs. The analysis finds two observable variables that can be used to identify which children have a higher probability of becoming troubled youth: poverty and residing in rural areas. The analysis also finds that risky behaviors increase with age and differ by gender, thereby highlighting the need for program and policy differentiation along these two demographic dimensions. (author's)
Lancet. 2007 Sep 22; 370(9592):1032-1033.Cost-effectiveness analysis, as referenced by Davide Mauri and Nikolaos Polyzos, constitutes one of several sources of information considered by policymakers in developing and developed worlds in making decisions about the optimum efficient use of health-care resources. The WHO Commission on Macroeconomics and Health has suggested that interventions costing less than three times a country's per capita gross domestic product per disability-adjusted life year gained can be regarded as good value, and analysts have equivalently applied this threshold to analyses that use quality-adjusted life years (QALYs). Preliminary results from a cost-effectiveness analysis of vaccination with quadrivalent HPV 6/11/16/18 vaccine in Mexico suggest a cost/QALY ratio well below this threshold in that country. Previous analyses in developed world settings have consistently shown that vaccination of girls and young women has a cost-effectiveness ratio within the range typically regarded as cost-effective. In countrieswith the fewest resources, direct assistance and public-private partnerships can help deliver needed medicines to the population at or below development costs-eg, the ivermectin donation for river blindness. Marc Arbyn states that if the cases of vaccine-type-related disease are subtracted from disease due to all types, there are a larger number of cases in women who received vaccine than in those who received placebo. This subtraction assumes that the subset of disease cases due to vaccine HPV types and the subset of cases due to non-vaccine HPV types are mutually exclusive, which is not the case. Coinfections with vaccine and non-vaccine types are common. In the presence of coinfection, the effect of such a subtraction is to ignore the presence of non-vaccine HPV types in disease where a vaccine-type HPV has also been detected. The effect of the subtraction is to preferentially attribute co-infected disease cases only to the vaccine HPV types. Individuals in the placebo group are more likely to have their non-vaccine type-related disease discounted in this way. Owing to the high efficacy of the vaccine, individuals in the vaccine group have less vaccine-type-related disease, and so those in the vaccine group have fewer such coinfection cases. To illustrate this point, an analysis of the numbers of individuals with disease due to vaccine and non-vaccine HPV types in the intention-to-treat population of protocols 013 and 015 is presented in the figure. The parts shaded blue would be the result of subtraction, similar to Arbyn's subtraction. However, the total numbers of cases of disease related to non-vaccine HPV types are 226+56=282 cases in the vaccine group and 193+106=299 cases in the placebo group. There is not an excess of cases caused by non-vaccine HPV types in the vaccine group. (full text)
[Unpublished] 2007. Presented at the 2007 Annual Meeting of the Population Association of America, New York, New York, March 29-31, 2007. 18 p.The Joint United Nations Programme on HIV/AIDS (UNAIDS) has developed the Estimation and Projection Package (EPP) for making national estimates and short term projections of HIV prevalence based on observed prevalence trends in antenatal clinics. Understanding uncertainty in its projections and related quantities is important for more informed policy decision making. We propose using Bayesian melding to assess the uncertainty around the EPP predictions. Prevalence data as well as information on the input parameters of the EPP model are used to derive probabilistic HIV prevalence projections - a probability distribution on a set of future prevalence trajectories. We relate antenatal clinic prevalence to population prevalence and account for variability between clinics using a random effects model. Predictive intervals for clinic prevalence are derived for checking the model. We discuss predictions given by the EPP model and the results of the Bayesian melding procedure for Uganda where prevalence peaked at around 28% in 1990; the 95% prediction interval for 2010 ranges from 1% to 7%. (author's)
Orphans and vulnerable children affected by HIV / AIDS in Brazil: where do we stand and where are we heading?
Revista de Saude Publica / Journal of Public Health. 2006 Apr; 40 Suppl:23-30.This study aimed at identifying human rights' status and situation, as expressed in the United Nations General Assembly Special Session on HIV/AIDS, of children and adolescents living with HIV/AIDS, non-orphans and orphans affected by AIDS, based on local and international literature review. The main study findings did not allow to accurately estimating those children and adolescents living with HIV and non-orphans affected by HIV/AIDS but data was available on those living with AIDS and orphans. The limitations and possibilities of these estimates obtained from surveillance systems, mathematical models and surveys are discussed. Though studies in literature are still quite scarce, there is indication of compromise of several rights such as health, education, housing, nutrition, nondiscrimination, and physical and mental integrity. Brazil still needs to advance to meet further needs of those orphaned and vulnerable children. Its response so far has been limited to providing health care to those children and adolescents living with HIV/AIDS, preventing mother-to-child HIV transmission and financing the implementation and maintenance of support homes (shelters according to Child and Adolescent Bill of Rights) for those infected and affected by HIV/AIDS, either orphans or not. These actions are not enough to ensure a supportive environment for children and adolescents orphaned, infected or affected by HIV/AIDS. It is proposed ways for Brazil to develop and improve databases to respond to these challenges. (author's)
Achieving the Millennium Development Goals in sub-Saharan Africa: a macroeconomic monitoring framework.
World Economy. 2006; 29(11):1519-1547.3,000 Africans die every day of a mosquito bite. Can you think about that, malaria? That's not acceptable in the 21st century and we can stop it. And water-borne illnesses - dirty water takes another 3,000 lives - children, mothers, sisters . . . If we're to take this issue seriously, and we must, because in 50 years, you know, when they [G-8 Heads of State] look back at this moment . . . they'll talk about what we did or didn't do about this continent bursting into flames. It is the most extraordinary thing to watch people dying three in a bed, two on top and one underneath, as I have seen in Lilongwe, Malawi. I mean, it is an astonishing thing. And it's avoidable. It's an avoidable catastrophe. You saw what happened with the tsunami. You see the outpouring, you see the dramatic pictures. Well, there's a tsunami happening every month in Africa, but it's an avoidable catastrophe. It is not a natural calamity. (author's)
East African Medical Journal. 2006 Jan; 83(1):1-3.At the Millennium Summit in September 2000, world leaders adopted the United Nations Millennium Declaration, which included attainment of the eight Millennium Development Goals (MDGs) by 2015. The first seven MDGs are aimed at reducing poverty and promoting human development while the eighth MDG recognises the essence of global partnership in achieving the first seven. The three MDGs directly related to health (MDGs 4-6) are interdependent so concerted efforts are needed to achieve them. (excerpt)
Potential impact of antiretroviral therapy on HIV-1 transmission and AIDS mortality in resource-limited settings.
Journal of Acquired Immune Deficiency Syndromes. 2006 Apr 15; 41(5):632-641.The objective was to estimate the potential impact of antiretroviral therapy on the heterosexual spread of HIV-1 infection and AIDS mortality in resource-limited settings. A mathematic model of HIV-1 disease progression and transmission was used to assess epidemiologic outcomes under different scenarios of antiretroviral therapy, including implementation of World Health Organization guidelines. Implementing antiretroviral therapy at 5% HIV-1 prevalence and administering it to 100% of AIDS cases are predicted to decrease new HIV-1 infections and cumulative deaths from AIDS after 10 years by 11.2% (inter-quartile range [IQR]: 1.8%-21.4%) and 33.4% (IQR: 26%-42.8%), respectively. Later implementation of therapy at endemic equilibrium (40% prevalence) is predicted to be less effective, decreasing new HIV-1 infections and cumulative deaths from AIDS by 10.5% (IQR: 2.6%-19.3%) and 27.6% (IQR: 20.8%-36.8%), respectively. Therapy is predicted to benefit the infected individual and the uninfected community by decreasing transmission and AIDS deaths. The community benefit is greater than the individual benefit after 25 years of treatment and increases with the proportion of AIDS cases treated. Antiretroviral therapy is predicted to have individual and public health benefits that increase with time and the proportion of infected persons treated. The impact of therapy is greater when introduced earlier in an epidemic, but the benefit can be lost by residual infectivity or disease progression on treatment and by sexual disinhibition of the general population. (author's)
Methods and procedures for estimating HIV / AIDS and its impact: the UNAIDS / WHO estimates for the end of 2001.
AIDS. 2003 Oct 17; 17(15):2215-2225.Background: The Joint United Nations Programme on HIV and AIDS (UNAIDS) and the World Health Organization (WHO) have produced country-specific estimates of HIV/AIDS biannually since 1997. These estimates are a primary source of information about the extent and spread of the HIV/AIDS epidemic and its impact. The importance of having comparable country-specific estimates of HIV/AIDS is growing as estimates are used to determine how international resources to fight HIV/AIDS will be allocated to countries. Objectives: This paper describes the procedures and process used to make the 2001 round of UNAIDS/WHO estimates of HIV/AIDS. The paper focuses on the different approaches used to make estimates of prevalence in countries with generalized and low-level and concentrated epidemics as well as on new curve-fitting software that was developed to produce epidemic curves for each country. In addition, it presents the assumptions used (e.g. survival from infection to death, the rate of mother-to-child transmission) that are required to derive estimates of incidence and mortality in adults, as well as prevalence, incidence and mortality in children. Conclusion: The paper describes the general process by which the estimation and modelling procedures have been refined and improved over time. The paper also discusses the limitations and weaknesses of the procedures and the data used to make the estimates, and suggests areas where further improvements need to be made. (author's)
In: Evaluation and development: proceedings of the 1994 World Bank conference, edited by Robert Picciotto and Ray C. Rist. Washington, D.C., World Bank, 1995. 61-75. (World Bank Operations Evaluation Study)This paper presents a macroeconomic framework for evaluating the effects of policy-based adjustment programs, with an illustration from a recent World Bank structural and sectoral adjustment lending evaluation, and offers guidelines on the design of conditionality. The framework is designed for situations in which an estimated model of the economy is not available. It is basically a version of Robert Mundell's policy assignment model, which assigns policy instruments to targets following the principle of comparative advantage. The paper focuses on a cross-country application of the framework and begins with a discussion of the assignment model. The example, which draws from World Bank experience in adjustment lending in 55 countries, strongly indicates that when a macro framework is introduced early in the design of an economic adjustment program and decisions on policy are guided by the framework, the policy instruments are more likely to have their intended impact and their results are more likely to be sustainable. This paper also includes a general discussion on the design of adjustment programs, including a section on the structure of loan conditionalities.
Lancet. 1998 Dec 12; 352(9144):1886-91.Short-course chemotherapy is currently the most effective treatment for most patients with tuberculosis (TB), and direct observation helps many patients complete the 6-8 month treatment regimen. Passive case finding is recommended for a number of reasons. The authors developed an age-structured mathematical model to explore the characteristics of TB control under the World Health Organization (WHO)-recommended directly-observed treatment, short-course (DOTS) strategy, and to forecast the effect of improved case finding and cure upon TB epidemics for each of the 6 WHO regions. In countries in which the incidence of TB is stable and HIV-1 absent, a control program which reaches the WHO targets of 70% case detection and 85% cure would reduce the incidence rate of TB by 11% per year and the death rate by 12% per year. However, if the incidence of TB has been declining for some years, the same case detection and cure rates would have a smaller effect upon incidence. DOTS saves a greater proportion of deaths than cases, and that difference is larger in the presence of HIV-1. HIV-1 epidemics cause an increase in TB incidence, but do not substantially reduce the preventable proportion of cases and deaths. Without more active efforts to control TB, the annual incidence of the disease is expected to increase by 41% between 1998 and 2020, from 7.4 to 10.6 million cases per year. Achieving WHO targets by 2010 would, however, prevent 23% of cases by 2020.
[A model of world population growth as an experiment in systematic research] Model' rosta naseleniya zemli kak opyt sistemnogo issledovaniya.
VOPROSY STATISTIKI. 1997; (8):46-57.A mathematical model was developed for the estimation of global population growth, and the estimates were compared with those of the UN and covered the stretch of 4.4 million years B.C. to the years 2175 and 2500 A.D. The estimates were also broken down into human, geological, and technological historical periods. The model showed that human population would stabilize at the level of 14 billion around 2500 A.D. and 13 billion around 2200 A.D., in accordance with UN projections. It also revealed the history of human population growth through the following stages (UN figures are listed in parentheses): 100,000, about 1.6 million years ago; 5 (1-5) million, 35,000 B.C.; 21 (10-15) million, 7000 B.C.; 46 (47) million, 2000 B.C.; 93 (100-230) million, at the time of Christ; 185 (275-345) million, 1000 A.D.; 366 (450-540) million, 1500 A.D.; 887 (907) million, 1800 A.D.; 1158 (1170) million, 1850 A.D.; 1656 (1650-1710) million, 1900 A.D.; 2812 (2515) million, 1950 A.D.; 5253 (5328) million, 1990 A.D.; 6265 (6261) million, 2000 A.D.; 10,487 (10,019) million, 2050 A.D.; 12,034 (11,186) million, 2100 A.D.; 12,648 (11,543) million, 2150 A.D.; 12,946 (11,600) million, 2200 A.D.; and 13,536 million, 2500 A.D. The model advanced the investigation of phenomena by studying the interactions between economical, technological, social, cultural, and biological processes. The analysis showed that humanity has reached a critical phase in its growth and that development in each period depended on external, not internal, factors. This permits the formulation of the principle of demographic imperative (distinct from the Malthusian principle), which states that resources determine the speed and extent of the growth of population.
In: Methodology for population studies and development, edited by Kuttan Mahadevan, Parameswara Krishnan. New Delhi, India, Sage, 1993. 82-121.Migration can be obligatory (transfers in job, joining husbands place) or sequential (the movement of dependents), besides being voluntary. The major data sources for the study of migration are population censuses, sample surveys, and population registers. A continuous population registration system has been in existence in the Scandinavian countries, a few West European countries, Taiwan, Israel, Japan, and some East European countries. Developed countries have developed techniques of estimating migration without sample surveys by using other sources built in within their social system. The censuses are the most widely used data sources for migration research where direct questions on migration (place of birth, place of last residence, place of residence at a specific prior date, and duration of residents) set the focus on the volume, level and pattern, differential selectivity, origin, and destination. Migration can be measured by the direct (census or sample survey) and indirect (residual methods from vital statistics and survival ratios based on census and/or life table) approaches. Selectivity in migration deals with differences in migration related to age, sex, marital status, education, occupation, ethnic origin, and language. Other topics addressed include determinants of migration; statistical generalizations and laws (Ravenstein's laws, push-pull theory); typologies; economic, spatial, behavioral, and mathematical approaches in migration theory; Zelinsky's hypothesis of migration/mobility transition; and the demographic, economic, and social consequences of migration. The migration process in multidimensional, time and space specific, thus a single theory is not comprehensive enough to explain its dynamics. Instead, a series of theories can be formulated: theory of migration for peasants, theory of migration for intellectuals, and theory of migration for cultural groups. This necessitates the development of comprehensive typologies of migration.
BULLETIN OF THE WORLD HEALTH ORGANIZATION. 1993; 71(3-4):421-8.Worldwide coverage of measles vaccine is about 80%, but many communities and countries have considerably lower coverage rates. WHO is concerned about measles occurring in infants between 6 and 12 months old, especially in densely populated African cities. Measles rarely occurs in infants under 6 months old, but the measles case fatality rate is greatest in the 1st year of life. WHO aims for an effective measles vaccine to be administered at 6 months old. A high titer vaccine appears to reduce survival among children receiving it. Some countries have reduced measles incidence by as much as 90% by achieving coverage levels greater than 90% with a single dose measles vaccine. Another method to prevent early measles cases and later vaccine failures is administration of the 1st dose around 6 months and a 2nd dose no earlier than 12 months. Measles vaccine policy in the US and some countries in Europe is routine 2-dose measles schedules: 1st dose between 12-19 months and 2nd dose at school entry. This schedule is appropriate in developed countries with good immunization coverage. Other countries schedule the 1st dose anywhere between 6-9 months and the 2nd dose between 12 months and 7 years. All mathematical models of the effects of 2-dose schedules indicate that 2-dose schedule are a great benefit. The literature shows that developing countries with high immunization coverage and well-managed immunization programs can effectively execute and sustain 2-dose measles schedules. Measles vaccination early in life sometimes results in a blunted antibody response. The 2-dose schedules are probably more expensive than 1-dose schedules and require more cold storage space. No field trials have looked at clinical efficacy of 2-dose measles schedules in developing countries. Ideal field trials would be randomized controlled trials. Demonstration projects can evaluate operational issues, e.g., dropout rates, cost, and vaccine usage. Case control studies can address technical and epidemiological issues.
FAMILY PLANNING WORLD. 1992 Nov-Dec; 2(6):8.Policy and program planners use information gained from computer-based statistical models to develop interventions against AIDS. Models of the epidemic's effect, however, show widely differing impacts on population. With the recent entry of a British researcher's view of the impact of AIDS on the population of Africa, the debate between researchers has only intensified. While the World Health Organization (WHO) has conservatively estimated that 40 million people will be infected with HIV by the year 2000, Roy Anderson of the University of London and Robert May of Oxford University expect AIDS to cause population decline in Africa after the year 2002. Major donors and researchers feel that while population growth rates will decline, growth rates will not turn negative due to AIDS. The British researchers, however, do not consider their views to differ greatly from those of US researchers, but they do have problems with overly conservative WHO projections. Their research assumes a higher degree of transmission between core groups of HIV-positive people, including prostitutes, IV drug users, and general populations in Africa's hardest hit areas. They project infection prevalence to reach 50% or more in some areas. Greater levels of prostitution and poverty, as well as the tendency for males to have sex with increasingly younger females, will lead to higher HIV incidence and prevalence in Africa. Family planning experts are voicing their concern over the integrity of these models and question whether they are more than simply educated guesses of what the future holds. Even though projections are uncertain and extremely data-dependent, family planning efforts must continue. Whether or not the AIDS pandemic eventually levels off in certain areas, critics must remember that family planning improves maternal and child health in addition to contributing to lower growth rates and prevent AIDS.