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Thursday, January 4 — Session 4: Epidemiology
11:40 am-noon	Romulus Breban UCLA Email: breban@ucla.edu authors: Romulus Breban, Raffaele Vardavas and Sally Blower, The Semel Institute for Neuroscience and Human Behavior, David Geffen School of Medicine, University of California, Los Angeles, California 90095-1555 Inductive Reasoning Games as Influenza Vaccination Models: Mean Field Analysis Yields Border-Collision Bifurcations We define and analyze an inductive reasoning game of voluntary yearly vaccination in order to establish whether or not a population of individuals acting in their own self-interest would be able to prevent influenza epidemics. Our results show that epidemics are rarely prevented. We also find that severe epidemics may occur without the introduction of pandemic strains. Furthermore, we address the situation where market incentives are introduced to help ameliorating epidemics. Surprisingly, we find that vaccinating families not only does not qualitatively change the epidemiological dynamics, but also increases the frequency of severe epidemics. However, a public health program requesting prepayment of vaccinations may significantly ameliorate influenza epidemics by changing the epidemiological dynamics through border-collision bifurcations.
noon-12:20 pm	James York Univ. Maryland Email: yorke2@ipst.umd.edu HIV - Can we save thousands of lives? How infectious a person infected with HIV is depends upon what stage of the disease the person is in. By "infectiousness", we mean for this talk, the probability of transmitting the infection in one sexual contact of individuals not involved in a long-term relationship with each other, and not under treatment for HIV. Measurements are indirect and any analysis of this question must involve non-linear dynamics. The results should affect public health policies in countries like the U.S. and the U.S. has just changed its policies. In our study we use three stages before the onset of AIDS: primary, latent and (non-AIDS) symptomatic. Everyone agrees that the latent stage is has low infectivity, but how do primary and symptomatic compare? The answer is controversial. We find that the infectivity of the symptomatic stage is at least as high as primary, and it is usually about 8 times as long, so our results mean this stage is the most dangerous, the one in which the most transmissions are likely to occur. The answers in the literature, like our results, depend on a heavy analysis of the data since direct experiments are impossible, but the mathematical detail will not be presented. Implications of our infectivity estimates and modeling for understanding heterosexual epidemics such as in the U.S. and Sub-Saharan Africa are explored. The results I will discus have appeared in J. AIDS in collaboration with Brandy L. Rapatski and Frederick Suppe.

 

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