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Reinfection thresholds and the management of recurrent infections

Final Activity Report Summary - REINFECTIONTHRESHOLD (Reinfection thresholds and the management of recurrent infections)

The project develops a conceptual framework to study the global epidemiology of infectious diseases. The reinfection threshold concept, introduced by the team leader to indicate the transmission potential required for disease persistence in a population of partially immune individuals, underlies a phenomenological transition in epidemic dynamics whose manifestations depend on disease specificities. We challenged conclusions obtained with previous models and formulate new explanations for field observations.

Our research combines two transversal axes:
1. To increase the accuracy and practical value of the reinfection threshold by focusing on specific infections;
2. To perform comparative studies across different infections, extract general trends, and standardise concepts for use in public health practice.

We establish a pivotal role for the reinfection threshold in a range of infectious diseases. In tuberculosis, we note that communities that sustain transmission intensities above threshold are generally insensitive to vaccination. In pertussis, we attribute the recent resurgence of the disease in developed countries to a decrease in transmission. In malaria, we identify a threshold for elimination in regions of low to moderate transmission intensity. In diseases caused by antigenically diverse pathogens, such as influenza and dengue, a reinfection threshold has a destabilizing effect that favours polymorphism.

More generally, we develop conceptual models for the ecology and evolution of infectious diseases and construct quantitative models of pathogen transmission, diversification and selection, which may be further developed as tools in the design of medical interventions. Finally, we propose laboratory experiments to test specific ideas from theoretical epidemiology.

The team has been engaged in fostering and implementing public databases and interdisciplinary research in epidemiology, and raising public awareness for the diversity of scientific research associated with infectious diseases.