Biomedical subjects

Elamin H Elbasha

Publications and source records attributed to Elamin H Elbasha.

9 recordsLinked to original sources

PubMed2006

Mathematical models for predicting the epidemiologic and economic impact of vaccination against human papillomavirus infection and disease.

Infection with human papillomavirus (HPV) is the primary cause of cervical cancer, other anogenital cancers, genital warts, and recurrent respiratory papillomatosis. Clinical studies have demonstrated that a prophylactic HPV vaccine can prevent infection, genital warts, and the precancerous lesions that lead to cervical cancer. Given the absence of data on the long-term effectiveness of HPV vaccination, a number of mathematical models have been developed to provide insight to policy makers by projecting the long-term epidemiologic and economic consequences of vaccination and evaluate alternative vaccination policies. This paper reviews the state of these models. Three types of HPV mathematical models have been reported in the literature: cohort, population dynamic, and hybrid. All have demonstrated that vaccination can significantly reduce the incidence of cervical cancer in the long term. However, only the cohort and hybrid models have evaluated the cost-effectiveness of vaccination strategies for preventing cervical cancer. These models have generally shown that vaccinating females can be cost-effective. None has accounted for the potential benefits of vaccinating the population to reduce the burden of recurrent respiratory papillomatosis and cancers of the vagina, vulva, anus, penis, and head/neck. Given that only the population dynamic model can account for both the direct and indirect (i.e., herd immunity effects) benefits of vaccination in the population, future research should focus on further development of dynamic models by expanding the range of epidemiologic outcomes tracked and including the ability to assess the cost-effectiveness of alternative vaccination policies.

Cost-Benefit Analysis↗

PubMed2006

Theoretical assessment of public health impact of imperfect prophylactic HIV-1 vaccines with therapeutic benefits.

This paper presents a number of deterministic models for theoretically assessing the potential impact of an imperfect prophylactic HIV-1 vaccine that has five biological modes of action, namely "take," "degree," "duration," "infectiousness," and "progression," and can lead to increased risky behavior. The models, which are of the form of systems of nonlinear differential equations, are constructed via a progressive refinement of a basic model to incorporate more realistic features of HIV pathogenesis and epidemiology such as staged progression, differential infectivity, and HIV transmission by AIDS patients. The models are analyzed to gain insights into the qualitative features of the associated equilibria. This allows the determination of important epidemiological thresholds such as the basic reproduction numbers and a measure for vaccine impact or efficacy. The key findings of the study include the following (i) if the vaccinated reproduction number is greater than unity, each of the models considered has a locally unstable disease-free equilibrium and a unique endemic equilibrium; (ii) owing to the vaccine-induced backward bifurcation in these models, the classical epidemiological requirement of vaccinated reproduction number being less than unity does not guarantee disease elimination in these models; (iii) an imperfect vaccine will reduce HIV prevalence and mortality if the reproduction number for a wholly vaccinated population is less than the corresponding reproduction number in the absence of vaccination; (iv) the expressions for the vaccine characteristics of the refined models take the same general structure as those of the basic model.

AIDS Vaccines↗

PubMed2005

Risk aversion and uncertainty in cost-effectiveness analysis: the expected-utility, moment-generating function approach.

The availability of patient-level data from clinical trials has spurred a lot of interest in developing methods for quantifying and presenting uncertainty in cost-effectiveness analysis (CEA). Although the majority has focused on developing methods for using sample data to estimate a confidence interval for an incremental cost-effectiveness ratio (ICER), a small strand of the literature has emphasized the importance of incorporating risk preferences and the trade-off between the mean and the variance of returns to investment in health and medicine (mean-variance analysis). This paper shows how the exponential utility-moment-generating function approach is a natural extension to this branch of the literature for modelling choices from healthcare interventions with uncertain costs and effects. The paper assumes an exponential utility function, which implies constant absolute risk aversion, and is based on the fact that the expected value of this function results in a convenient expression that depends only on the moment-generating function of the random variables. The mean-variance approach is shown to be a special case of this more general framework. The paper characterizes the solution to the resource allocation problem using standard optimization techniques and derives the summary measure researchers need to estimate for each programme, when the assumption of risk neutrality does not hold, and compares it to the standard incremental cost-effectiveness ratio. The importance of choosing the correct distribution of costs and effects and the issues related to estimation of the parameters of the distribution are also discussed. An empirical example to illustrate the methods and concepts is provided.

Cost-Benefit Analysis↗

PubMed2005

Inequalities in self-reported physical health in the United States, 1993-1999.

This study investigated inequalities in physically healthy days in the United States during 1993-1999, by socioeconomic and demographic group. The generalized entropy GE(2) and other indices were computed using data from the Behavioral Risk Factor Surveillance System survey, 1993-1999. The results indicate that GE(2) for the US population increased by 17% during 1993-1999. Low-to-middle income groups had the highest increases in inequalities during this time (51-66%), whereas the least educated, Asian/Pacific Islanders, American Indians/Alaska Natives, the oldest, the youngest, and the richest had the lowest (-14-10%). In 1999, inequalities ranged from 0.0153 (income>or=$50 000) to 0.112 (income<$10 000). Inequalities have increased during 1993-1999 and vary substantially across groups. The American Indians/Alaska Natives experienced the highest inequalities whereas Asians/Pacific-Islanders exhibited the lowest inequalities. More attention should be given to within-group inequalities.

Adolescent↗

PubMed2005

Vaccination against multiple HPV types.

Vaccines against the most common human papillomavirus (HPV) types are currently under development. Epidemiologic data suggest that the transmission dynamics of different HPV types are not independent. Some studies indicate that interactions among HPV types are synergistic, where infection with one type facilitates concurrent or subsequent infection with another HPV type. Other studies point to antagonistic interference among HPV types. Here we develop a mathematical model to explore how these interactions may either enhance or diminish the effectiveness of vaccination programs designed to reduce the prevalence of the HPV types associated with cervical cancer. We analyze the local stability of the infection-free and boundary equilibria and characterize the conditions leading to a coexistence equilibrium. We also illustrate the results with numerical simulations using realistic model parameters. We show that if interactions among HPV types are synergistic, mass vaccination may reduce the prevalence of types that are not even included in the vaccine.

Female↗

PubMed2005

Assessing the annual economic burden of preventing and treating anogenital human papillomavirus-related disease in the US: analytic framework and review of the literature.

The anogenital human papillomavirus (HPV) is estimated to be the most commonly occurring sexually transmitted infection in the US. Comprehensive estimates of the annual economic burden associated with the prevention and treatment of anogenital HPV-related disease in the US population are currently unavailable. The purpose of this paper is to (i) outline an analytic framework from which to estimate the annual economic burden of preventing and treating anogenital HPV-related disease in the US; (ii) review available US literature concerning the annual economic burden of HPV; and (iii) highlight gaps in current knowledge where further study is particularly warranted. Among eight US studies identified that describe the annual economic burden pertaining to one or more aspects of anogenital HPV-related disease, three met the review eligibility criteria (published between 1990 and 2004, examined multiple facets of annual anogenital HPV-related economic burden, and clearly articulated the data and methods used in the estimation process). All costs were adjusted to 2004 US dollars. Estimates of the annual direct medical costs associated with cervical cancer were comparable across studies (range 300-400 million US dollars). In contrast, there was a wide range across studies for estimates of the annual direct medical costs associated with cervical intraepithelial neoplasia (range 700 million US dollars-2.3 billion US dollars). Only one study reported direct medical costs for anogenital warts (200 million US dollars) and routine cervical cancer screening (2.3 billion US dollars). No studies examined direct medical costs attributable to HPV-related anal, penile, vaginal or vulvar cancers, or the work and productivity losses resulting from time spent receiving medical care, morbidity or mortality. Current economic burden estimates would suggest annual direct medical costs associated with the prevention and treatment of anogenital warts and cervical HPV-related disease of at least 4 billion US dollars. This figure would likely rise to at least 5 billion US dollars per year if direct medical costs associated with other disease entities caused by the sexual transmission of HPV were included, with further additions to the economic burden totalling in the billions of dollars if work and productivity losses were incorporated, a research priority for future studies.

Costs and Cost Analysis↗

PubMed2004

Cost-effectiveness analysis and health care resource allocation: decision rules under variable returns to scale.

We argue that health programs are administered in settings that often violate the frequently stated assumption of constant returns to scale in the provision of health services. Three types of returns to scale are identified from the general economic literature: returns to scale with respect to population, effectiveness, and quality. We show that decision rules based on incremental cost-effectiveness ratios or cost-benefit tests are not optimal if returns to scale are not constant. We derive the optimal decision rules under variable returns to scale using optimization techniques, and employ several examples to illustrate the concepts and methods.

Cost-Benefit Analysis↗

PubMed2003

Deadweight loss of bacterial resistance due to overtreatment.

Widespread use of antibiotics is considered the major driving force behind the development of antibiotic resistance. The benefits of exceeding the welfare-maximizing level of antibiotic use are below the costs of resistance created by this excess quantity of antibiotics used, thereby resulting in a welfare deadweight loss. This paper uses a simple economic model to examine the theoretical and empirical aspects of the welfare loss generated by resistance and analyzes its policy implications. The annual deadweight loss associated with outpatient prescriptions for amoxicillin in the United States is estimated at US dollars 225 million.

Amoxicillin↗

PubMed2003

Preferences and person trade-offs: forcing consistency or inconsistency in health-related quality of life measures?

We consider assumptions about preferences implicit in the person trade-off exercises used to derive health-related quality of life measures for the Global and US Burden of Disease Projects. Because these methods and their results have the potential of being adopted by other researchers, a critical review of this methodology and its assumptions is warranted. Exercise participants are told that quality of life valuation is approached using two different questions to reveal logical inconsistencies in each person's responses. An inconsistency is claimed to exist if a participant's two responses violate a particular mathematical relationship, and participants are forced to modify their responses to satisfy that relationship. We demonstrate that this supposed 'logical' relationship need not hold for logically consistent, rational individuals, and we prove that the relationship will in fact hold only for a particular class of social value functions exhibiting two characteristics that may not be consistent with the preferences of some participants. These results imply that the forced modification may invalidate some responses, as it may require some participants to provide final answers that are inconsistent with their true preferences. We then discuss preference characterizations in the existing person trade-off literature, from which this relationship may have been derived.

Attitude to Health↗