Scientists at the Instituto Gulbenkian de Ciencia (IGC), in Portugal, together with colleagues at the Universities of Lisbon and Warwick, in the United Kingdom, have developed a mathematical model that explains why the tuberculosis (TB) vaccine is ineffective in many of the developing countries. The model quantifies the predicted decrease in the number of TB cases in light of both the socioeconomic development of a population and the characteristics of new vaccines. Their research has been published in the Proceedings of the Royal Society (22nd March edition).
The efficacy of the bacille Calmette-Guérin (BCG) vaccine (the only vaccine in current use against tuberculosis) is variable, and there is no consensus about its usefulness. Estimates of protection range from 80% in the United Kingdom to around 0% in India, for example. For 30 years now scientists have tried to unravel the role of socioeconomic, genetic and environmental factors in generating this broad range of protection. This new model highlights socioeconomic factors (namely population density, access to primary healthcare, sanitation and diet, amongst others), which influence the dissemination of the infeccious agent.
The scientists estimate that the efficacy of the BCG vaccine decreases as the number of cases of TB increases, leading to a positive feedback loop, whose effect becomes most evident when the transmission potential reaches the reinfection threshold (a newly-defined concept). Other factors are expected to be involved, but no other model to date has been able to reproduce the magnitude of observed trends.
Ana Coutinho | alfa
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