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Collective Dynamics

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http://hdl.handle.net/10400.7/28

Collective dynamics is an integrating component of natural systems, fundamental to all sciences, from physics to biology and sociology. We seek any unifying principles underlying the forms of self-organization in large populations of interacting elements. Our approach combines mathematical and experimental systems.

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Browsing Collective Dynamics by advisor "Proceedings. Biological sciences, R.S."

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  • The reinfection threshold promotes variability in tuberculosis epidemiology and vaccine efficacy
    Publication . Gomes, M. G. M.; Franco, A. O.; Gomes, M. C.; Medley, G. F.; Proceedings. Biological sciences, R.S.
    Population patterns of infection are determined largely by susceptibility to infection. Infection and vaccination induce an immune response that, typically, reduces susceptibility to subsequent infections. With a general epidemic model, we detect a 'reinfection threshold', above which reinfection is the principal type of transmission and, consequently, infection levels are much higher and vaccination fails. The model is further developed to address human tuberculosis (TB) and the impact of vaccination. The bacille Calmette-Guérin (BCG) is the only vaccine in current use against TB, and there is no consensus about its usefulness. Estimates of protection range from 0 to 80%, and this variability is aggravated by an association between low vaccine efficacy and high prevalence of the disease. We propose an explanation based on three postulates: (i) the potential for transmission varies between populations, owing to differences in socio-economic and environmental factors; (ii) exposure to mycobacteria induces an immune response that is partially protective against reinfection; and (iii) this protection is not significantly improved by BCG vaccination. These postulates combine to reproduce the observed trends, and this is attributed to a reinfection threshold intrinsic to the transmission dynamics. Finally, we demonstrate how reinfection thresholds can be manipulated by vaccination programmes, suggesting that they have a potentially powerful role in global control
    2004-03Journal article Open access Show more