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An age-structured and behavioral model of measles dynamics in the United Kingdom

Student-Run Applied & Math Seminar

Speaker: Ricky Kwok, UC Davis
Location: 2112 MSB
Start time: Wed, Oct 14 2009, 12:10PM

Measles is a potentially fatal childhood disease, causing approximately 7-8 million deaths worldwide in the 1960's. After the introduction of the measles-mumps-rubella (MMR) vaccine in 1988, the number of deaths decreased to 197,000 in 2007. In the United States, public schools require children to be immunized with this vaccine in order to be enrolled. Elsewhere, in regions such as the United Kingdom, the decision to vaccinate is voluntary for parents. A consequence of this is lower uptake during a vaccine scare. If parents decide the payoff for immunity outweighs the risks of the vaccine, they will likely vaccinate. However, vaccine scares increase parents' perceptions of the risk, decreasing the likelihood of vaccinating. Parents also inform each other of their perceived risk of vaccine through social interactions. If they make their decisions through this method, then vaccine scares can spread through social learning. A high rate of social learning would be if parents switched strategies frequently upon interactions. We investigate the case how social learning spread the recent MMR scare initialized by a paper published in 1998. The paper raised the question whether or not the MMR vaccine caused autism. After the publication, there has been a drop in vaccine coverage in United Kingdom every year until 2003. A possible explanation for the phenomenon is the media coverage of the paper. This caused parents to choose not to vaccinate their children and also warn other parents. To model this situation, we use an SEIR model of disease dynamics. We add age structure to capture the higher contact rates among children observed in measles. Moreover, we incorporate how the vaccine scare affects parents' decisions to vaccinate through social learning. Our results show that when the social learning rate is high, measles prevalence can have high fluctuations in amplitude.