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A Multi-Cohort Markov Model of Anti-HPV Vaccination Programme.
- Giampiero Favato (29 April 2008)
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HPV: Predicting the Unpredictable and legally taking Liberty of Happiness
- Dr.Basavaraj Shivayogi Hadapad, Dr.Revathy Sheny, Assistant Professor of Biochemistry, Manipal University, Manipal-576104, India (7 May 2008)
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Giampiero Favato, Academic Fellow Henley Management College, Greenlands, RG9 3AU UK
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A large body of modelling studies has already been conducted to evaluate the cost-effectiveness of different vaccination strategies [1- 6].The cost-effectiveness of the anti-HPV vaccination has already been confirmed, although these studies have considered exclusively one cohort of women at different ages of immunisation plus an eventual additional “catch-up” cohort. We developed a partially dynamic model capable to simulate the probability of proceeding from one disease stage to the next one. A Markov model was based on a set of data imputed according to defined transition probabilities, which were function of population demographics and time- dependent characteristics of HPV infection An Italian multi-cohort vaccination strategy was estimated to involve in the first year 1,141,232 women in total, to progressively decrease to 295,062 women from a single cohort after a 6-year period. Compared to the control group, the multi- cohort vaccination strategy would induce a statistically significant relative risk reduction of respectively 63.1% (C.I. 95%: 62.4%-63.8%; p<0.001) and 60.3% (C.I. 95%: 58.7%-61.5%; p<0.001) in the 3 cohort and the 4 cohort scenarios [7] The results of combined assessments supported the cost/effectiveness of a 3-4 cohorts vaccination strategy. In order to optimise the use of public financial resources, a multi-cohort vaccination plan could be considered as promising point equilibrium between the need to accelerate the reduction of the prevalence of cervical cancer and the rational management of healthcare demand. Access to the vaccination plan should give priority to women at an age that is significant in terms of evolution of the disease [8]: 1. Adolescents aged 11 years: they are the primary candidate cohort, because presumably they have not been exposed to HPV. Ideally a preventive HPV vaccine should be administered prior to the first sexual intercourse. In clinical trials, the highest immune response to vaccine was shown in adolescents. 2. Young girls up to 18 years of age: the cohort of age that immediately precedes the peak of HPV infection. 3. Young women up to 26 years of age: they are already included in a wide nationally organized screening programme for cervical cancer, so access to the vaccination programme would offer them an efficient and synergistic primary prevention against cervical cancer. 1 A 3 cohorts vaccination strategy would provide a large proportion of the female population aged 11-25 years with a period of 6-7 years of cost/effective HPV coverage. During the subsequent phases of the vaccination plan, the decreasing costs associated with the treatment of low-grade and high-grade pre-cancer lesions and cervical cancer, as well as the costs of therapies for genital external lesions, would progressively compensate for the cost of the vaccine. When the time that separates the different cohorts elapses, the number of subjects eligible to be vaccinated would be equivalent to the first selected cohort of adolescents aged 11 years. References: 1. Sanders GD, and Taira AV. Cost Effectiveness of a potential vaccine for human papillomavirus. Emerging Infectious Diseases 2003; 9: 37 -48 2. Kulasingam SL, Myers ER. Potential health and economic impact of adding a human papillomavirus vaccine to screening programmes. JAMA 2003; 290: 781-789 3. Taira AV, Neukermans CP, and Sanders GD. Evaluating human papillomavirus vaccination programmes. Emerging Infectious Diseases 2004; 10: 1915-1923 4. Goldie SJ, Kholi M, Grima D, et al. Projected clinical benefits and costeffectiveness of a human papillomavirus 16/18 vaccine. Journal of the National Cancer Institute 2004; 96: 604-615 5. Barnabas RV, Laukkanen P, Koskela P, et al. Epidemiology of HPV 16 and cervical cancer in Finland and the potential impact of vaccination: mathematical modeling analyses. PLoS Medicine 2006; vol. 3(e138): 624-632 6. Elbasha EH, Dasbach EJ, and Insinga RP. Model for assessing human papillomavirus vaccination strategy. Emerging Infectious Diseases 2007; 13: 28-41 7. Favato, G, Pieri V, Mills R W. Analisi costo-efficacia del programma di vaccinazione anti-HPV in Italia: il modello multi-coorte Markov, Farmaci 2007, Vol. 31 – n2. 8. Ho GYF, Bierman R, Beardsley L, et al. Natural history of cervicovaginal papillomavirus infection in young women. The New England Journal of Medicine 1998; 338: 423-428. Competing interests: None declared |
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Dr.Basavaraj Shivayogi Hadapad, Associate Professor of Ayurveda Manipal University, Manipal - 576104, India, Dr.Revathy Sheny, Assistant Professor of Biochemistry, Manipal University, Manipal-576104, India
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Dear Editors Jo Waller and Jane Wardle Noble laureate Neils Bohr said, "It is very difficult to make an accurate prediction, especially about the future." In particular, statistical scientists cannot predict non linear human being, who will contract which disease, or who will respond to vaccination against HPV 16 & 18. “Human being is more immeasurably complex than any demonstrably chaotic system” says Professor William Firth. Senior Cancer epidemiologist assumed that NHS Cervical screening programme in women under 55 may have prevented 800 deaths in 1997 but Denis Burkitt wrote “To believe that doctors and hospitals help keep people healthy is plain rubbish”. In the NHS cervical screening programme around 1000 women need to be screened for 35 years to prevent one death! Screening programmes for Bone density, cervical cancer, plasma glucose, blood pressure, cardiac disorders, and lipid profile take liberty of happiness of healthy public and legally robs national treasure. It was predicted on U.S. FDA website that Gardasil is a “New vaccine, prevents cervical cancer” but death of 13 young girls and 3,461 adverse reactions proved that it is a drug to take liberty of life not to prevent cervical cancer. It was very surprising to note that the prospective cohort study on bivalent vaccine against Human Pappiloma Virus at Manchester, funded by pharmaceutical company has not noticed / or not seen (?) any adverse drug reaction (BMJ, on line first, 24th April 2008). At this moment I remember Douglas G Altman, Head of Medical Statistics Laboratory, London for his article on “The Scandal of Poor Medical Research” published in British Medical Journal. Associate Professor Joel Lexchin/ team concludes that Studies sponsored by pharmaceutical companies were more likely to have out comes favoring the sponsor. Most genital HPV infections are self limited, even those caused by high risk types. It usually takes more than 10 years between infection and development of cervical cancer. Long interval means mere infection may not be sufficient for progression to cancer and estimated 10 million new cases each year in the US will not develop cancer. It implies that cancer requires strong genetic susceptibility, low immunity, unhealthy diet / lifestyle and environmental influence. According Edward Lorenz, who died of cancer recently “very small changes can have large impacts” From September 2008, school girls aged between 12 or 13 years in the United Kingdom will routinely be offered vaccination against HPV with out knowing level of antibody required for protection of cervical cancer. National programmes should make an effective and preventive agenda to create fruitful awareness in younger generation to reduce number of sexual partners, to improve immunity, follow healthy diet / lifestyle and try for good environment. “People working in health care system should have non linear thinking to prevent health scare system”. Yours ever: Author Dr. Basavaraj Shivayogi Hadapad . References:1. W. J. Firth. Chaos – Predicting the Unpredictable. BMJ 1991; 303:1565- 1568, 2. http://cbs4.com/iteam/vaccine.gardasil.i.2.708105.html, 3. Douglas G Altman. The Scandal of Poor Medical Research. BMJ 1994; 308: 283 -284, 4. Joel Lexchin, Lisa A Bero, Benjamin Diulbegovic.Pharmaceutical industry sponsorship and research outcome and quality: systemic review. BMJ 2003; 326:1167-1170 Competing interests: None declared |
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