Eliane R. Rodrigues

Cost-Effectiveness Analysis of a Quadrivalent Human Papilloma Virus Vaccine in Mexico

BACKGROUND AND AIMS Cervical cancer is one of the main causes of death in women in low- and middle-income countries. Despite technological and scientific advances that allow an early detection of precancerous lesions and curative treatment of cervical cancer, Mexico and other Latin American countries have only been able to obtain a small decrease in the mortality rates for this kind of cancer. How to implement and sustain effective public health strategies for cervical cancer prevention, such as increasing cytology-based screening program coverage and implementing HPV-DNA testing and vaccination, are important questions. The aim of this study is to perform a cost-effectiveness analysis of the introduction of a quadrivalent (HPV 6/11/16/18) HPV vaccine into the public health system and evaluate the epidemiological and economic benefits on prevention of cervical cancer in Mexico. METHODS A Markov model is used to simulate the natural history of HPV infection in a cohort of Mexican women to evaluate the cost-effectiveness of the cervical cancer screening strategy used in Mexico as well as the benefits of other potential strategies such as 1) vaccination only, 2) conventional cytology-based screening program only and 3) vaccination followed by screening. For the strategies that involve screening we have chosen screening intervals of 3 and 5 years. The model produces results that are reasonably close to the epidemiological data related to HPV and cervical cancer in Mexico. RESULTS The quadrivalent HPV vaccine could reduce the probability of persistent HPV-16/18 infection by at least 60%, which would result in a near-proportional reduction in HPV-16/18-associated invasive cervical cancer and CIN 3. CONCLUSIONS The strategy of using only vaccination (

Maximum a posteriori estimation of the daily ozone peaks in Mexico City

45 USD for three doses) as a preventive measure was a very cost-effective strategy in Mexico (

Non-homogeneous Poisson models with a change-point: an application to ozone peaks in Mexico city

68USD/LYS). The strategy of vaccination with traditional screening of Pap test every 3 years produced higher cost by a lower performance of cervical cytology in Mexico, at a cost of

Modeling environmental noise exceedances using non-homogeneous Poisson processes.

15,935 USD per life-year. The cost-effectiveness of the vaccination strategy was highly sensitive to age of vaccination, duration of vaccine efficacy, and cost of vaccination. The Mexican model predicts that a quadrivalent HPV vaccine will reduce the incidence of high- and low-risk-associated cervical cancer. A program of vaccination as a preventive strategy is likely cost effective. The results of this study could be of great value in decision-making for the implementation of an HPV vaccine as a public health policy in Mexico provided that the cost of each dose will be, at most,

Expected population weight and diabetes impact of the 1-peso-per-litre tax to sugar sweetened beverages in Mexico

15 dollars (USD) dollars, combined with HPV testing, the new strategy of national secondary prevention program.

A Gibbs Sampling Algorithm to Estimate the Occurrence of Ozone Exceedances in Mexico City

Exposure to high levels of pollution is a persistent problem in large cities throughout the world. The ability to predict the occurrence of a high level of a pollutant allows environmental authorities to take preventive measures, such as controlling the emission of pollution. Communities and officials can also take actions to reduce the exposure of susceptible groups in the population. Therefore, being able to estimate the behavior of a given pollutant is of great importance. In this article we use a Markov chain model to study this behavior. In order to do so, we consider the sequence of the daily maximum measurements of a pollutant and let successive intervals containing them follow a Markov chain of order K>-0. The novelty here is that we allow K to be a random variable and estimate it and the corresponding transition probabilities using a maximum a posteriori method. The results are used to perform estimations about the behavior of ozone levels in Mexico City.

Using stochastic volatility models to analyse weekly ozone averages in Mexico City

In this paper, we use some non-homogeneous Poisson models in order to study the behavior of ozone measurements in Mexico City. We assume that the number of ozone peaks follows a non-homogeneous Poisson process. We consider four types of rate function for the Poisson process: power law, Musa–Okumoto, Goel–Okumoto, and a generalized Goel–Okumoto rate function. We also assume that a change-point may or may not be present. The analysis of the problem is performed by using a Bayesian approach via Markov chain Monte Carlo methods. The best model is chosen using the DIC criterion as well as graphical approach.

Applications of discrete-time Markov chains and poisson processes to air pollution modeling and studies

In this work a non-homogeneous Poisson model is considered to study noise exposure. The Poisson process, counting the number of times that a sound level surpasses a threshold, is used to estimate the probability that a population is exposed to high levels of noise a certain number of times in a given time interval. The rate function of the Poisson process is assumed to be of a Weibull type. The presented model is applied to community noise data from Messina, Sicily (Italy). Four sets of data are used to estimate the parameters involved in the model. After the estimation and tuning are made, a way of estimating the probability that an environmental noise threshold is exceeded a certain number of times in a given time interval is presented. This estimation can be very useful in the study of noise exposure of a population and also to predict, given the current behavior of the data, the probability of occurrence of high levels of noise in the near future. One of the most important features of the model is that it implicitly takes into account different noise sources, which need to be treated separately when using usual models.

Weibull and generalised exponential overdispersion models with an application to ozone air pollution

Study question What effect on body mass index, obesity and diabetes can we expect from the 1-peso-per-litre tax to sugar sweetened beverages in Mexico? Methods Using recently published estimates of the reductions in beverage purchases due to the tax, we modelled its expected long-term impacts on body mass index (BMI), obesity and diabetes. Microsimulations based on a nationally representative dataset were used to estimate the impact of the tax on BMI and obesity. A Markov population model, built upon an age-period-cohort model of diabetes incidence, was used to estimate the impact on diagnosed diabetes in Mexico. To analyse the potential of tax increases we also modelled a 2-peso-per-litre tax scenario. Study answer and limitations Ten years after the implementation of the tax, we expect an average reduction of 0.15 kg/m2 per person, which translates into a 2.54% reduction in obesity prevalence. People in the lowest level of socioeconomic status and those between 20 and 35 years of age showed the largest reductions in BMI and overweight and obesity prevalence. Simulations show that by 2030, under the current implementation of 1-peso-per-litre, the tax would prevent 86 to 134 thousand cases of diabetes. Overall, the 2-peso-per-litre scenario is expected to produce twice as much of a reduction. These estimates assume the tax effect on consumption remains stable over time. Sensitivity analyses were conducted to assess the robustness of findings; similar results were obtained with various parameter assumptions and alternative modelling approaches. What this study adds The sugar-sweetened beverages tax in Mexico is expected to produce sizable and sustained reductions in obesity and diabetes. Increasing the tax could produce larger benefits. While encouraging, estimates will need to be updated once data on direct changes in consumption becomes available.

A Stochastic Model for Transport of Particulate Matter in Air: An Asymptotic Analysis *

Inhabitants of many cities around the world suffer the effects of high levels of ozone air pollution. When the ozone concentration stays above the threshold of 0.11 parts per million (0.11ppm) for a period of one hour ormore, a very sensitive part of the population (e.g. elderly and newborn) in that environment may experience serious health deterioration (Bell et al., 2004, 2005, 2007; Gauderman et al., 2004; Loomis et al., 1996; O’Neill et al., 2004; WHO, 2006). Therefore, being able to predict when exceedances of the 0.11ppm threshold (or any threshold above this value) may occur is a very important issue. Depending on the country, different thresholds may be considered to declare environmental alerts. The US Environmental Protection Agency (US-EPA) has established as its standard that the three-year average of the fourth highest daily maximum 8-hour average ozone concentration measured at each monitor within an area over each year must not exceed 0.075ppm (see EPA, 2008). In the case of Mexico, the standard is 0.11ppm and an individual should not be exposed, on average, for a period of an hour or more (NOM, 2002). In Mexico City when the ozone concentration surpasses the threshold 0.2ppm an emergency alert is issued and measures are taken to prevent population exposure to the pollutant (see http://www.sma.df.gob.mx). It is possible to find in the literature a large number of works focussing on the study of the behaviour of air pollutants in general. Among the ones related to ozone air pollution we may quote, Horowitz (1980), Roberts (1979a, 1979b), Smith (1989) considering extreme value theory; Flaum et al. (1996), Gouveia & Fletcher (2000), Kumar et al. (2010), Lanfredi & Macchiato (1997) and Pan & Chen (2008) using time series analysis; Alvarez et al. (2005) and Austin & Tran (1999) considering Markov chain models; Achcar et al. (2008b, 2009a, 2009b) using stochastic volatility models; and Huerta & Sanso (2005) with an analysis of the behaviour the maximummeasurements of ozone with an application to the data fromMexico City. Davis (2008) and Zavala et al. (2009) present studies that analyse the impact on air quality of the driving restriction imposed in Mexico City. When the aim is to estimate the number of times that a given environmental standard is surpassed, Raftery (1989) and Smith (1989) use time homogeneous Poisson processes to model 8